Where does the late George H.W. Bush rank in the history of the American presidency? Historical judgments are best left to historians who can appraise a president most accurately, often decades after his death.

There is a convincing case to be made, however, that Bush was one of the greatest global leaders of all our presidents.

I admit to a bias, as I worked for him as an advisor on Soviet affairs at the White House's National Security Council for the last 2½ years of his presidency. Yet his achievements on the world stage were the most important of any president during the last half century. In just one term in office, from 1989 to 1993, he was the indispensable leader in ending the Cold War peacefully as the Soviet Union collapsed and 15 new states took its place in December 1991. Bush was the major figure in unifying Germany in the NATO alliance following the fall of the Berlin Wall.

He also organized an extraordinary global coalition to defeat Saddam Hussein in the 1990-91 Gulf War. He then presided over the creation of the modern Middle East peace negotiations between Israel and the Palestinians later that year. And we shouldn't forget that his administration conceived of the North American Free Trade Agreement and handed it over to President Bill Clinton, who secured congressional approval early in his presidency.

On their own, each of these achievements would be considered consequential for any president. Together, they represent an extraordinary collection of successes that made America and the world more stable and peaceful.

It wasn't a given, however, that the Cold War would end peacefully. In fact, we worried inside the U.S. government about all sorts of crises that might unfold as the Soviet Union neared its eventual collapse on Christmas Day 1991. A cabal of KGB and Red Army leaders actually overthrew Soviet leader Mikhail Gorbachev for two suspenseful days in August of that year.

We worried there might be another challenge to Gorbachev and Russian Republic President Boris Yeltsin again that autumn which could provoke conflict inside the country or seek to obstruct the freedom of the USSR's former satellites in Eastern Europe. We were also acutely concerned that the USSR's vast collection of nuclear weapons and nuclear material might fall into the hands of a breakaway warlord across that vast country or into the hands of a criminal network.

Bush's singular achievement was in creating a relationship of trust with both Gorbachev and Yeltsin. That reassured them the U.S. would not seek to take advantage in the Cold War's last months.

It was also not a given that West and East Germany would unify peacefully as communism collapsed after the fall of the Berlin Wall in November 1989. British Prime Minister Margaret Thatcher and French President Francois Mitterrand, both with clear memories of the Second World War, were initially skeptical as they pondered the reappearance of a powerful German state in the center of Europe. Some German leaders advocated a reunited neutral Germany between Russia and the West.

Bush knew both of those scenarios would be destabilizing. He was looking to the future and so he swung his support behind German Chancellor Helmut Kohl's aim for a united German nation — but one embedded in the NATO alliance.

It was also not a given that a U.S.-led coalition would be able to defeat Saddam Hussein's army without major U.S. and allied casualties. Bush worked the phone for months to persuade an unprecedented collection of Arab, European, Asian and North American countries to pull together over 700,000 allied forces under U.S. and Saudi leadership. Saddam was driven from Kuwait and defeated with a surprisingly low level of allied casualties.