Conquering a land is not as simple as winning battles. Julius Caesar had to park his troops in various hostile neighborhoods and deal with repeated uprisings until the natives there could be beaten into submission and resolve to accept Roman yoke because resisting it would be too fatal.
Conquering a land is not as simple as just moving in and beating people up. Even after battles are won, the local people must accept your rule. If not, you will have to deal with uprisings like Julius Caesar did as he undertook his effort to conquer Gaul.