Robert Gates, the man who has effectively led and managed the world’s largest military force for the past four and half years, had a simple message as he stepped back into civilian life — the United States may have the most powerful and gifted military on the planet but that power could lose its luster if future presidents plunge the country into “wars of choice.” In other words, if you find yourself a part of the Joint Chiefs of Staff or in the inner corridors of the White House, make sure you learn the lessons of the past before sending American soldiers to fight another war halfway around the world.

For a defense official who served Republican administrations for most of his forty-plus years in government, the message may seem strange. The Republican Party, after all, traditionally prides itself on being “tough” on matters related to national security. Yet Gates’ affiliation with Republicans is also why his words should be taken seriously. After a long and hard decade of never ending combat in Iraq and Afghanistan, the men and women serving the American military are stretched to the breaking point. Gates may not say it out in the open for fear of being chastised but he clearly recognizes that the United States are not as resilient as they used to be.

Throughout his career as defense secretary, Gates was seen as both a problem solver and a “fixer.” A well established character within the American intelligence community with a solid reputation, he was tapped by President George W. Bush to lead the Pentagon in the midst of one of the most tumultuous times in the nation’s history. By the time Gates was nominated to the post in the autumn of 2006, the war that the Bush Administration had gambled most of its credibility on was spiraling out of control. Thousands of Iraqi civilians, Sunni and Shia alike, became the main victims in a barrage of violence from rival militia groups, predatory policemen and militants affiliated with the Al Qaeda brand. While the Bush White House denied it outright numerous times, Iraq was looking more and more like a civil war. Donald Rumsfeld, who led the Pentagon at the time, seemed detached from what was going on.

The situation, both in Iraq and in the Pentagon, needed to change. And it needed to change as soon as possible. Thus after a tough nomination process in front of the Senate Armed Services Committee, Gates went into his office and started the difficult work of turning the war around and rebuilding the strength and soft power appeal of the United States. Generals and commanders who were previously safe from reprimands were fired for poor performance while junior officers who were courageous enough to think “outside the box” were awarded promotions in the hopes of spurring a new wave of innovation within the Army and Marine Corps.

Perhaps more significant than anything else, Gates made sure that he was close to the president but not so close as to jeopardize his credibility as impartial and fair to dissenters. President Bush certainly benefited from Gates’ more temperate demeanor as did Barack Obama.

Gates, of course, was not perfect. For one, he was a main reason for President Obama to sidestep Marine Corps General James E. Cartwright as next chairman of the Joint Chiefs of Staff. Many of the goals that Gates sought to accomplish while at the Defense Department either proved to be too difficult to solve or were left untouched. Although the Pentagon is now starting to find savings in order to cut its $700 billion budget, defense spending is still vastly more than it needs to be at a time when Washington is attempting to cut government spending anywhere it can. Robert Gates also leaves behind three wars — Afghanistan, Iraq, Libya — with the one that he is most identified with — Iraq — still plagued by insurgent violence, suicide bombings and assassinations.

Just as Robert Gates came into the Pentagon with a lot on his plate, so too will his replacement, Leon Panetta. The stereotypical Washington insider, Panetta enters the office facing a host of challenges, many of which will take decades to solve. As Gates found out time and again, trying to break through the status quo, whether by cutting the size of the defense budget or decommissioning a missile defense shield, has the affect of stirring resistance from at least someone on Capitol Hill.

One thing is certain, said Gates. If the United States do not find a way to stop embroiling themselves in war for war’s sake, none of these problems will be as serious as the trouble that could pop up in the future.