I'm pretty sure (1.) is A, and I know for a fact that (3.) is D because slavery was a regular practice between quarreling tribes. I have no clue what (2.) is. Best of luck.
Answer:
Conquistadors
Explanation:
Conquistadors are there to take over whatever land they have
C, coal changed the game and increased production by increasing speed and efficiency.
The soviet union because they were most affected by the war
