In the mid 80’s two guys wrote a book called “Remember the Alamo”.
It involved a wealthy dying oil tycoon who has pretty much perfected time travel. H feels that he, if he can send people back to Alamo to change the outcome of the battle, would be in a position to eventually occupy oil fields that are just south of the current Texas-Mexico border.
The people he sends back are Vietnam vets and mercenaries. he plans on winning the battle with claymore mines and automatic weapons.
All in all, it was a good book with a few twists and turns that keep the reader interested.
Harry Turtledove did a book where South African have a time machine and send AK-47 back to the Confederate forces in the Warring Americans Period.
Logistics are a big factor again - as they are in all conflicts...