I think the 2nd answer is correct
I think it is Trench warfare.
C
promote a balance of power
<span>In 1803, President Thomas Jefferson commissioned the Corps of Discovery, and named U.S. Army Captain Meriwether Lewis its leader, who selected William Clark as his partner.Their goals were to explore the Louisiana Purchase, establish trade and U.S. sovereignity over the native peoples along the River Missouri.</span>
Answer would be D. sovereignty