The most febrile of George W. Bush haters liked to claim during his tenure that the former president "scared" them. There is far more reason to be frightened by President Barack Obama, because fecklessness and inconstancy trigger wars.
The outstanding example of weakness inviting aggression was the conduct of the democracies toward Adolf Hitler in the 1930s. Though it has been retroactively tainted as shameful cowardice, the policy of appeasement grew out of a "war weariness" that was far more understandable than our own. Britain and France suffered millions of dead and wounded in World War I and were desperate to avoid a repeat. The Munich Agreement, which ceded part of Czechoslovakia to Germany (without its consent), was signed by Britain and France in hopes that Hitler's ambitions were limited, but in any case because they believed appeasement was the best way to avoid war.
They couldn't have been more wrong. Hitler didn't, to put it mildly, share their abhorrence of war. He welcomed it (when he was sufficiently strong) and he interpreted their appeasement policy as weakness. They'd forgotten the Roman axiom: "If you want peace; prepare for war." In the end, they had to fight anyway, but only after permitting their enemy valuable time. Had the United States not been dragged into the war by Japan's attack and Hitler's declaration of war on us, the Axis powers would almost certainly have won.
In June of 1961, President John F. Kennedy met with Soviet Premier Nikita Khrushchev. The communist sized up the young president as callow and unimpressive. Kennedy said later that it was "the worst thing in my life. He savaged me." Eighteen months later, the world was plunged into a nuclear crisis as Kennedy was forced to respond to the USSR's placement of intermediate-range missiles in Cuba. Khrushchev had concluded that Kennedy could be rolled. The resulting showdown brought the world close to nuclear war.
In July of 1991, April Glaspie, U.S. ambassador to Iraq, met with Saddam Hussein and asked very politely why he had so many divisions parked on the border of Kuwait. Later in the same meeting, she said, "We have no opinion on your Arab/Arab conflicts, such as your dispute with Kuwait. Secretary (James) Baker has directed me to emphasize the instruction ... that the Kuwait issue is not associated with America." A few weeks later, Iraq invaded and conquered Kuwait, prompting former President George H.W. Bush to launch a war to liberate it. Glaspie said later, "Obviously, I didn't think, and nobody else did, that the Iraqis were going to take all of Kuwait."