For the record to Joseph W, Canada and Britain more or less won the War of 1812, since the US launched an invasion of canada where you burned down our parliament, but were eventually pushed back by canadian militia and british troops. After Napoleon was put down in Europe, the british essential put the US back in there place by burning down the White House. Had the British wanted to, they easily could have taken back the colonies. But at that point, it wasnt in there best interest.
Also in WW2, by the time the Americans entered the war, since they sat out the first 2 years selling weapons and technology to both sides, the americans were dragged into the war. At which point the British had already suceeded in breaking the german air invasion on the british isles. And the key to British success was actually the fact that there allies (New Zealand, Canada and Australia) were sending massive amounts of troops and supplies to help the british. In all likely hood the events of WW2 would have ended the same, since Russia would have eventually have slowed the germans down and new technological developments (T-34) would have been put into proper use. The US only really helped hurry the end of the war. the Invasion of Europe likely would have been an attack on southern france and likely a bit later in the war when the Germans had pulled most of there strength to the eastern front.
Now on to the real question about american imperialism. For the last 20 years, the US has lost its right to call itself the best country to live in for a few reasons, but mainly the development of the socialist states in Norway, Sweden, Iceland, Canada and a few others. The only reason why the US is as powerful as it is now, is because they had the advantage of being out of WW2 while the rest of the world was busy fighting, this allowed there economy to outgrow the other countries easily, and since the US mainland was never attacked, they never suffered any real damage to there industry. This allowed the US to dominate the post war world with its powerful economy. At this point US corruption is visible to everyone, the War in Iraq is the best point to use, where companies like Haliburton are given massive contracts simply because the Vice-Pres has alot of friends there. The US has even manager to destroy its own economy with the US war since china now has the power at anytime to destroy the US dollar since it has close to 1 Trillion US bonds and could choose to sell them for pennies, devaluating the US dollar and likely putting the US back into a mass recession. The only hope you honestly have is to elect another clinton and pull out of iraq, atleast then your economy wont collapse.