I don't think they NEED to start wars to boost business. I DO think that they think it's easier to go that route though. Not precisely start wars, but to have an "enemy" they can threaten people with if they don't do what they say.
It's a form of extortion. Normally, people won't stand for the government threatening them directly, but if the government creates an enemy and claims that it is the ENEMY who will do terrible things to them if they don't do something, then they neatly avoid any kind of outrage the people might direct at them. The Soviets were that enemy for a long time, but when the Soviet Union fell, we started casting about for a new enemy to keep everyone in line. Now it's a nebulous term called "Terrorism" Terrorism is better than the Soviets. It can survive any one nation falling apart. The terrorists will simply move to a new country and set up shop. If we don't like that country, we can use terrorism as an excuse to make them do what we want by threatening to go in and get the terrorists without their cooperation. If it's a nation we DO like, then we can play on their sympathies and get them to do what we want or "the terrorists win"
At home, we invade the personal lives of everyone, we wear down our citizens rights by using words like "security" and phrases like "The War on Terror" If we don't give up our rights, they say then we are irresponsibly vulnerable to an attack. The number of deaths from the Trade Tower attacks is inconsequential in the big picture when you put it up against deaths caused by almost any other single source. However, put those deaths on the same day and in the same place and suddenly it becomes the biggest threat to anyone..... EVER.
I have to ask the question, because no one else seems willing to ask it: When do we get our rights back now that we've given them away? It is perhaps the most important question right now, and NO ONE is asking it. If we go by history, the answer is emphatically: Never.... and that is (at least for me) simply unacceptable.