Exhibit A The Zodiac Killer, who terrorized the Bay Area during the late 1960s and early 1970s, was never caught. He used to write to the police at length about his crimes. (Among the many things wrong with Zodiac, he gave himself that nickname. Dude, you can't give yourself a nickname.) Now, how did he choose his victims? Apparently, at random. The first few were all couples in isolated areas, couples going to some or another kind of "Makeout Point." One could suppose that those particular couples were bothering him, and that's why he chose them. They were in a place where he didn't want them to be, doing things he didn't want them to do. He killed them in response to something they'd done.
Exhibit B Japan is an island nation. After the United States forced Japan to open up to international trade (a gold star for whomever can tell me the year without looking it up), the Japanese embarked upon a rapid and frighteningly efficient process of modernization. (For more information, look up the Meiji Restoration.) The Japanese did this to resist the imperialist domination that had befallen so many other parts of Asia. However, as I said before, Japan is an island nation, and poor in natural resources. So, in order to stand on their own two feet, the Japanese needed more resources. In the Sino-Japanese War of 1895, Japan seized Korea and Taiwan from Imperial China. In 1931, Japan seized Manchuria, declaring it the puppet state of Manchukuo. In 1937, they invaded China proper, setting off a series of events that culminated in Pearl Harbor, Iwo Jima, and Hiroshima/Nagasaki. The Chinese had resources the Japanese wanted. So, the Japanese took what they wanted, killing any Chinese they had to in order to do it.
Thus My well-meaning but terribly misguided friend SNL asks, "But don't you think terrorists often act, at least in some part, because of American policies?" By that logic, the Zodiac Killer acted, at least in some part, because he didn't like his victims. By your logic, Scott, the Japanese acted, at least in some part, because the Chinese wouldn't give them what they wanted. Yes, terrorists do act, at least in some part, because of American policies. That does not mean we are not blameless. To give you another example, Timothy McVeigh murdered 168 people in Oklahoma City because he opposed the federal government. To say that al Qaeda is just reacting to American policy is to say that McVeigh's victims were responsible for their own murders; after all, most of them worked for the federal government that he so hated.
And now, because it is never a bad time to shine the light of knowledge into the darkness of ignorance, I give you the most famous words of George Santayana: "Those who cannot remember the past are condemned to repeat it."