Well to help ya out:
"Has martial law been declared?" There is no government. Not applicable

"What's the governments presence like throughout the country and in Philly?" Diminished to a point of splintering. Single force remains, no way of long range communication exists. 

"Will we encounter US military?" If someone wants to create a faction that is a remnant of the US military then you will. The point of solidarity I will hammer home is that no one knows. That is why I am being this absent on the subject. If you were an individual in this time period all you would know is that "things went to shit". I'll change the opening OOC, but to be specific, this is about 60+ years after said collapse of society. 

"Has the whole world gone to shit or is this an isolated United States incident?" Unknown to denizens of Philadelphia.

"Lastly, can I make two factions? I wanted to create a sort of political organization that is pretty large, with tens of thousands of members scattered throughout the country. But it's essentially NPC's. While the faction that I would be playing as, would be allied muscle of this organization, comprised of 20-50 members give or take in the Philadelphia area."

Sure go ahead, just pm me the CS before you post it.