Osama and his followers did not go to america to convert Christians to Islam at any point of time...
Let me enlighten you a bit here...there is 2 very distinct separate group of islamists...1 which goes about trying to convert people as there are christian and Buddhist missionaries... and another group that feels that islam is in danger and the enemy is America and its supporters and thinks it is waging a Jihad against it...
I do not agree with both....but thats the fact.
Also as Punjabis and assamese in a majority do not support terrorism, in the same way Muslims do not support terrorism....Please understand Muslims are more than 20% of world population...if all of them were terrorist you would not find them so hard to find, you wont have to go to the caves in Afghanistan for them.