Israel was not aggressive

Notice how multiple times Israel openly asked permission to cross the land, offering to pay if they drank water from the wells and it was only after the rollers of those land choose to come out in battle rather than allow them to cross the land that Israel was commanded to slay them and their people. The Lord did not clear the land of righteous people in order to give it to His chosen people; he cleared the land of people who were unwilling to even cross paths peacefully with another people.