Why don't we need 52% of the world's military spending. There is a large difference between our spending and the spending China per person due to the fact that the average Chinese still only makes $2K/year. The average American makes $46K a year. There is also the fact that our equipment tends to be more expensive, because of the higher value we place on personal life. Targetting military spending is like saying that if you have a dog, you aren't going to feed it and asking "why does it need to be fed".
We have a military because other countries have armed forces and thus the only way to ensure they don't attempt to attack us is to have our own.
As far as wars of Aggression.
I'm thinking that we haven't actually gotten involved in any wars of aggression.
The current Iraq War can be viewed as just a continuation of a prior conflict (1991 - Gulf War, which turned into the No Fly Zone missions (1991 - 2003) which turned into the current War (2003 - ...).
The War in Afghanistan was the direct result of another nation providing aid and comfort to an enemy, and refusing to recognize our legitimate security interests.
Yes, I can understand they were objecting based upon Muslim Hospitality, but if your neighbor was harboring some one that robbed your house, would you not enter your neighbor's house to root them out if the neighbor refused to give them up?
How about, we cut the salary of the president to $40K/yr, the salary of the Senators to $20K/yr, and reduce the salaries of all government officials in proportion to those figures.
That should take a large chunk out of the federal deficit and enable us to actually pay off our debt.