Maybe it's not simply the individual

Stephen Walt thinks we spend too much time discussing and analyzing world leaders, rather than also considering the circumstances in which they operate. Perhaps, this is because we have a tendency to want to keep things simple and believe that a country will change if the leaders change. For example, we see the Russia-Ukraine situation as basically Putin's baby. But, given the reality of history, the expansion of NATO, ballistic missile defense, the Anti-Ballistic Missile Treaty, Kosovo, and the weak Russian economy, would Medvedev do much different? Walt points out that leaders as varied as Adolf Hitler, Woodrow Wilson, Kim Il Sung, Indira Gandhi, Anwar Sadat, George W. Bush, and François Hollande have caused crises or started wars.
He concludes:

None of this is to say that individuals don't matter at all or that we shouldn't try to understand how Putin, Xi Jinping, Shinzo Abe, or other leaders see the world. But if we want to grasp the larger forces that drive global trends and ignite occasional crises, we'd be better off leaving that style of analysis to People magazine -- which is really good at that sort of thing -- and focus more of our attention on power, interests, and strategy.