One scary thought is these smaller objects we've been seeing for decades are not scientistic drones from another world, but reconnaissance drones that are probing the planet for minerals useful to them. That could be why they're constantly seen in nutrient-dense areas, stalking military units, and circling nuke locations.
Maybe they're monitoring us until their main fleet arrives, documenting our military advancements. It could literally take their main fleet decades or longer to arrive at near light speed because the distance is so great. Maybe these drones we see that appear like plasma orbs are faster, light speed so they've been here longer.
I know it sounds like a movie, but the idea that we're being set up for conquer is not impossible. The theory that Steven Hawkin suggested by the poster above isn't impossible. It's a very "human" scenario way of thinking obviously, but not out of the realm of possibility considering the increased likelihood that these objects aren't from Earth.
I honestly think the only tactic needed against us it to park a massive vessel in the skyline out of reach of nukes, and leave it there for months/weeks. We'd literally tear each other apart in fear.