(Okay, this is going to get ranty and probably more than a bit gratuitous)
You do realize how difficult that would be right? You aren't talking about a gorilla campaign on your own turf where you have a sizable portion of the population backing you up.
You're talking invading a thoroughly modernized nation with literally 100s of ethnic groups, none of which particularly like you. But lets ignore the modern military and police forces you'd encounter for 1 moment. How the fuck do you plan on getting here.
Logistics is a pain in the ass, its pretty easy sneaking a few people yeah, but try moving an army. You know why people say the US is the most powerful nation on earth? I'll give you a hint, it isn't the size or strength of our army.
We can move our armies anywhere in the world in a matter of days, with air support, tanks, food, water, fuel, covert ops, artillery, bomb squads, robots, and the kitchen sink.
Go ahead and try to get the same results, we'll wait.
Then you have another big issue, our modern military. See, once you're over here, you won't exactly have the hearts and minds of the people. No hiding for you. You'll be fighting on our terms, which means out in the open, where we can blow the fuck out of you. We have an awful big military that was structured to take on the Soviet Union. You'd be fighting exactly the kind of conflict we've been built for.
If you even set foot in a city, you'll have every Tom, Dick, and Harry just itching to pull the trigger on their penis enhancer. They won't be kind. You'll probably even convince pacifists and people fairly left of center to go buy rifles. We don't like you either.
Then you're left with still another problem, how the fuck do you plan on feeding and fueling your army if it hasn't already died. See, supply lines suck, and you have no experience with them. Armies move on their stomachs.
Let's give you the benefit of the doubt, you make a beach head in Virginia near D.C. How long do you think you can hold out to make your advance, and if its longer than a few days, how the fuck do you plan on feeding everyone and getting more ammo?
In short, come get us fucker, truth be told, we'd much rather you come to us than the other way around. We've been chasing fucks like you around since the 50's, its about time you can to us. It'd be a nice quick end to the whole thing.