Complex sentence: The nationalists, on the other hand, was overconfident and did not modify their strategy quickly enough, resulting in their failure, which had serious consequences later on as their communist enemy had successfully stabilized their rear area when winning the campaign.
Split into simpler sentences: The nationalists, on the other hand, were overconfident and did not modify their strategy quickly enough, resulting in their failure. This had serious consequences later on as their communist enemy had successfully stabilized their rear area when winning the campaign.