The Jews at the time of Our Lord's mission rejected him as the Messiah precisely because he was not what they wanted.
We as Christians hope for salvation, for a place with in Him in paradise. Not to attempt to bring about paradise here upon the earth.
War is a truly terrible thing, but it is not the only terrible thing. Consider the killing fields of Cambodia, southern Sudan, Tibet and indeed the Iraq of Saddam Hussein. Zimbabwe is not at war, but the Government kills and maltreats whole sections of the population. China is not at war but look to its actions in Tibet. In Argentina, formerly one of the richest in S America there is no war but a catastrophic financial collapse. Still the World Bank and the IMF are holding a whip hand over the Government there. In peacefull America how many unborn children are killed, black folk are forcibly kept away from voting in a presidential election. How many starve or go without clean water, and yet they do not live in a 'war zone'. Even in the wealthiest country in the world, how many are homeless, without adequate housing or healthcare while others enjoy a lifestyle beyond imagination?
As to the United States role, this seems complex. It is the greatest extant power. Its people are approximately 5% of the world's population and it gobbles up 25 percent of its resources. It is responsible, together with its coalition partners, for the killing of far more people than the 3000 killed on 11 September, 2001. Of course, you must understand most of this is something we call 'collateral' damage - so dishonest are we that we cannot call it for what it is. At the same time it has not made the world a safer place, rather the contrary. At home it has seen the drastic erosion of hard won civil liberties and with remarkably little effective debate. Between us, the coalition powers, we appear to have done an arguable job with the war, and made a mess of the peace.
I share Michael's horror of war. It is not that long ago I put my long handled mirror away and stopped looking under the car for any sign the vehicle had been tampered with. In the north of Ireland so-called paramilitaries still run 'protection' rackets, drug supply and knee-cap or worse those they deem transgressors. Some of those same folk draw salaries and/welfare benefits from a state they don't recognise. This is peace.
Peace-keeping operations often involve foreign soldiers who sit in their camps and fail to protect the vunerable around, because their 'rules of engagement' don't allow it.
Poor folks sons and daughters find themselves thousands of miles from home and in mortal danger, while the children of the great and good stay home and carry on as all was well with the world.
None of this makes a lot of sense. Some will spout on about progress. But heaven on earth ain't about to happen and anyone who believes that is somewhat detached from reality, sadly.