Ringo wrote a series of "Aliens invade Earth" books, which are fun reading. Earth gets notice from one group of aliens that a huge group of heavily armed, but not terribly bright, humanoid lizard (The Posleen) types are coming to take over the planet and eat everyone (okay that's a pretty crude synopsis). Earth is able to outfit a small group of soldiers/Marines with sci-fi battle armor, but a lot of the books revolve around regular US military units fighting. The aliens also have technology to rejuvinate older people, so the US can bring back guys who fought in WWII through Vietnam.
The top book is about the Germans bringing back a Waffen SS unit because the germans are so short on combat vets.
The 2nd book is a new series, don't know much about it.
In the first series there are running battles with the Posleen in Virginia, up to DC and into appalachians. A fair amount of two of the books, I think, revolve around a small unit of soldiers pursued by the Posleen who eventually meet up with (of course
) a relative of one of the other characters who is was a vietnam era green beret (I think) with a bunker filled with body armor, mres, Barretts, stacks of assault rifles etc. of course the 13 year old granddaughter ends up on her own in her little custom made suit of body armor with a .308 rifle fighting with the aliens in the mountains-they're fun reading.