On September 1st, 1939, Germany invaded Poland. This is what historians mark as the beginning of the Second World War. Just as in WWI, Britain needed America's aid in defending Europe against the Germans. However, the United States spent two blissful years simply producing and sending supplies to Britain. Only after the surprise attack on Pearl Harbor did the US help the ailing Brits and Soviets.
If America mobilized immediately and joined Great Britain and the Soviet Union the war very well could have been won much earlier. The powers that be at the top of our government recognized that. It has led to America's current policy--stick our nose in whomever's business want. Between our inaction of WWII and the breakout of the Cold War, the United States now attempts to officiate scrums all over the world.
It is no wonder that much of the world hates us--we can't keep to ourselves. In some cases it is perfectly clear that we must at least intervene, or announce our stance on an international issue. In others, however, we need to just let things play out, without criminalizing ourselves or being portrayed as a teenage girl who butts-in on other people's conversations.
America's attempt to make the world a better place may be successful, but at a cost. We are the World Police, and some countries hate us because of that.