From 1997 to 2000, he was commander-in-chief of the United States Central Command, in charge of all American troops in the Middle East. That was the same job held by Gen. Norman Schwarzkopf before him, and Gen. Tommy Franks after.
Following his retirement from the Marine Corps, the Bush administration thought so highly of Zinni that it appointed him to one of its highest diplomatic posts -- special envoy to the Middle East.
But Zinni broke ranks with the administration over the war in Iraq, and now, in his harshest criticism yet, he says senior officials at the Pentagon are guilty of dereliction of duty -- and that the time has come for heads to roll. Correspondent Steve Kroft reports.
"There has been poor strategic thinking in this," says Zinni. "There has been poor operational planning and execution on the ground. And to think that we are going to 'stay the course,' the course is headed over Niagara Falls. I think it's time to change course a little bit, or at least hold somebody responsible for putting you on this course. Because it's been a failure."
Zinni spent more than 40 years serving his country as a warrior and diplomat, rising from a young lieutenant in Vietnam to four-star general with a reputation for candor.
Now, in a new book about his career, co-written with Tom Clancy, called "Battle Ready," Zinni has handed up a scathing indictment of the Pentagon and its conduct of the war in Iraq.
In the book, Zinni writes: "In the lead up to the Iraq war and its later conduct, I saw at a minimum, true dereliction, negligence and irresponsibility, at worse, lying, incompetence and corruption."
"I think there was dereliction in insufficient forces being put on the ground and fully understanding the military dimensions of the plan. I think there was dereliction in lack of planning," says Zinni. "The president is owed the finest strategic thinking. He is owed the finest operational planning. He is owed the finest tactical execution on the ground. … He got the latter. He didn't get the first two."
Zinni says Iraq was the wrong war at the wrong time - with the wrong strategy. And he was saying it before the U.S. invasion. In the months leading up to the war, while still Middle East envoy, Zinni carried the message to Congress: "This is, in my view, the worst time to take this on. And I don't feel it needs to be done now."
But he wasn't the only former military leader with doubts about the invasion of Iraq. Former General and National Security Advisor Brent Scowcroft, former Centcom Commander Norman Schwarzkopf, former NATO Commander Wesley Clark, and former Army Chief of Staff Eric Shinseki all voiced their reservations.
Zinni believes this was a war the generals didn't want – but it was a war the civilians wanted.
"I can't speak for all generals, certainly. But I know we felt that this situation was contained. Saddam was effectively contained. The no-fly, no-drive zones. The sanctions that were imposed on him," says Zinni.
"Now, at the same time, we had this war on terrorism. We were fighting al Qaeda. We were engaged in Afghanistan. We were looking at 'cells' in 60 countries. We were looking at threats that we were receiving information on and intelligence on. And I think most of the generals felt, let's deal with this one at a time. Let's deal with this threat from terrorism, from al Qaeda."
One of Zinni's responsibilities while commander-in-chief at Centcom was to develop a plan for the invasion of Iraq. Like his predecessors, he subscribed to the belief that you only enter battle with overwhelming force.
But Secretary of Defense Donald Rumsfeld thought the job could be done with fewer troops and high-tech weapons.
How many troops did Zinni's plan call for? "We were much in line with Gen. Shinseki's view," says Zinni. "We were talking about, you know, 300,000, in that neighborhood."
What difference would it have made if 300,000 troops had been sent in, instead of 180,000?
"I think it's critical in the aftermath, if you're gonna go to resolve a conflict through the use of force, and then to rebuild the country," says Zinni.
"The first requirement is to freeze the situation, is to gain control of the security. To patrol the streets. To prevent the looting. To prevent the 'revenge' killings that might occur. To prevent bands or gangs or militias that might not have your best interests at heart from growing or developing."
Last month, Secretary Rumsfeld acknowledged that he hadn't anticipated the level of violence that would continue in Iraq a year after the war began. Should he have been surprised?
"He should not have been surprised. You know, there were a number of people, before we even engaged in this conflict, that felt strongly we were underestimating the problems and the scope of the problems we would have in there," says Zinni. "Not just generals, but others -- diplomats, those in the international community that understood the situation. Friends of ours in the region that were cautioning us to be careful out there. I think he should have known that."
Instead, Zinni says the Pentagon relied on inflated intelligence information about weapons of mass destruction from Iraqi exiles, like and others, whose credibility was in doubt. Zinni claims there was no viable plan or strategy in place for governing post-Saddam Iraq.
"As best I could see, I saw a pickup team, very small, insufficient in the Pentagon with no detailed plans that walked onto the battlefield after the major fighting stopped and tried to work it out in the huddle -- in effect to create a seat-of-the-pants operation on reconstructing a country," says Zinni.
"I give all the credit in the world to Ambassador Bremer as a great American who's serving his country, I think, with all the kind of sacrifice and spirit you could expect. But he has made mistake after mistake after mistake."
"Disbanding the army," says Zinni. "De-Baathifying, down to a level where we removed people that were competent and didn't have blood on their hands that you needed in the aftermath of reconstruction – alienating certain elements of that society."
Zinni says he blames the Pentagon for what happened. "I blame the civilian leadership of the Pentagon directly. Because if they were given the responsibility, and if this was their war, and by everything that I understand, they promoted it and pushed it - certain elements in there certainly - even to the point of creating their own intelligence to match their needs, then they should bear the responsibility," he says.
"But regardless of whose responsibility I think it is, somebody has screwed up. And at this level and at this stage, it should be evident to everybody that they've screwed up. And whose heads are rolling on this? That's what bothers me most."
Adds Zinni: "If you charge me with the responsibility of taking this nation to war, if you charge me with implementing that policy with creating the strategy which convinces me to go to war, and I fail you, then I ought to go."
Who specifically is he talking about?
"Well, it starts with at the top. If you're the secretary of defense and you're responsible for that. If you're responsible for that planning and that execution on the ground. If you've assumed responsibility for the other elements, non-military, non-security, political, economic, social and everything else, then you bear responsibility," says Zinni. "Certainly those in your ranks that foisted this strategy on us that is flawed. Certainly they ought to be gone and replaced."
Zinni is talking about a group of policymakers within the administration known as "the neo-conservatives" who saw the invasion of Iraq as a way to stabilize American interests in the region and strengthen the position of Israel. They include Deputy Defense Secretary Paul Wolfowitz; Undersecretary of Defense Douglas Feith; Former Defense Policy Board member Richard Perle; National Security Council member Eliot Abrams; and Vice President Cheney's chief of staff, Lewis "Scooter" Libby.
Zinni believes they are political ideologues who have hijacked American policy in Iraq.
"I think it's the worst kept secret in Washington. That everybody - everybody I talk to in Washington has known and fully knows what their agenda was and what they were trying to do," says Zinni.
"And one article, because I mentioned the neo-conservatives who describe themselves as neo-conservatives, I was called anti-Semitic. I mean, you know, unbelievable that that's the kind of personal attacks that are run when you criticize a strategy and those who propose it. I certainly didn't criticize who they were. I certainly don't know what their ethnic religious backgrounds are. And I'm not interested."
Adds Zinni: "I know what strategy they promoted. And openly. And for a number of years. And what they have convinced the president and the secretary to do. And I don't believe there is any serious political leader, military leader, diplomat in Washington that doesn't know where it came from."
Zinni said he believed their strategy was to change the Middle East and bring it into the 21st century.
"All sounds very good, all very noble. The trouble is the way they saw to go about this is unilateral aggressive intervention by the United States - the take down of Iraq as a priority," adds Zinni. "And what we have become now in the United States, how we're viewed in this region is not an entity that's promising positive change. We are now being viewed as the modern crusaders, as the modern colonial power in this part of the world."
Should all of those involved, including Rumsfeld and Wolfowitz, resign?
"I believe that they should accept responsibility for that," says Zinni. "If I were the commander of a military organization that delivered this kind of performance to the president, I certainly would tender my resignation. I certainly would expect to be gone."
"You say we need to change course -- that the current course is taking us over Niagara Falls. What course do you think ought to be set," Kroft asked Zinni.
"Well, it's been evident from the beginning what the course is. We should have gotten this U.N. resolution from the beginning. What does it take to sit down with the members of the Security Council, the permanent members, and find out what it takes," says Zinni.
"What is it they want to get this resolution? Do they want a say in political reconstruction? Do they want a piece of the pie economically? If that's the cost, fine. What they're gonna pay for up front is boots on the ground and involvement in sharing the burden."
Are there enough troops in Iraq now?
"Do I think there are other missions that should be taken on which would cause the number of troops to go up, not just U.S., but international participants? Yes," says Zinni.
"We should be sealing off the borders, we should be protecting the road networks. We're not only asking for combat troops, we're looking for trainers; we're looking for engineers. We are looking for those who can provide services in there."
But has the time come to develop an exit strategy?
"There is a limit. I think it's important to understand what the limit is. Now do I think we are there yet? No, it is salvageable if you can convince the Iraqis that what we're trying to do is in their benefit in the long run," says Zinni.
"Unless we change our communication and demonstrate a different image to the people on the street, then we're gonna get to the point where we are going to be looking for quick exits. I don't believe we're there now. And I wouldn't want to see us fail here."
Zinni, who now teaches international relations at the College of William and Mary, says he feels a responsibility to speak out, just as former Marine Corps Commandant David Shoup voiced early concerns about the Vietnam war nearly 40 years ago.
"It is part of your duty. Look, there is one statement that bothers me more than anything else. And that's the idea that when the troops are in combat, everybody has to shut up. Imagine if we put troops in combat with a faulty rifle, and that rifle was malfunctioning, and troops were dying as a result," says Zinni.
"I can't think anyone would allow that to happen, that would not speak up. Well, what's the difference between a faulty plan and strategy that's getting just as many troops killed? It's leading down a path where we're not succeeding and accomplishing the missions we've set out to do."
60 Minutes asked Secretary Rumsfeld and his deputy Wolfowitz to respond to Zinni's remarks. The request for an interview was declined.