Dude, the United States hasn't done anything remotely imperialistic since we ceded the Philippines. Every armed conflict in which we've engaged since WWI has either been to defend someone/something (WWI, WWII, Korean War, Vietnam War, Gulf War) or to forestall possible hostile action (Iraq War, Afghanistan).
Now, does it mean all of our military action ever conducted has been just? No. But the title of your meme irked me and I had to write this.