They had a massive advantage in tactical arms. Helicopters became coffins. Small arms isn’t going to do that...no matter how many Rambo movies you’ve seen.
The point remains, they took advantage of what they had and made the cost of occupation too high. In our country, should a democrat attempt to become a dictator and use the military to crack down on the people, there would not only be millions of small arms in the hands of millions of rednecks willing to hide in and strike from swamps and mountains, but there would also be mass defections from the military, including advanced weapons falling into the hands of said rednecks and highly trained soldiers who have trained on the very terrain they would now inhabit. It would not be a simple task and, should the will to remain free be strong enough, the cost of suppressing the people would be very high. I can see states seceding, asserting their autonomy, and military bases in their territory would fall into their control. Think of Texas and Florida seceding and all of the military hardware they have being used against the new dictator.
No, the best way to suppress the American people is to gradually acclimate them to dependency on the government for safety and basic necessities, then to find a scapegoat (usually the "rich") that can be blamed for problems to deflect attention from the government that is taking control over more and more parts of everyday life. At the same time, we need to put that same government deeper and deeper into debt, so the push becomes to continually raise taxes, to convince people that no one "needs" all that money they've worked a lifetime to accumulate, it's not fair that they can pass on wealth to their children, etc. Just make sure that no one seriously entertains the idea that government should actually spend LESS, not more.
And along with all of that, you need to keep pushing the narrative that no one should have guns, because reasons. They don't need one, big black scary looking guns are too dangerous, they're stupid for wanting guns, etc. At each step, you tighten the restrictions until the Constitution becomes meaningless and guns are rarely, if ever seen.
The ultimate goal is to transform the population into dependent, unarmed sheep, willing to accept whatever scraps their overlords give them and willing to fight to maintain the very oppression they're suffering. That's how you subjugate the American people.