Complex sentence: The fourth strategic miscalculation made by the retreating nationalist government was financial/economical: due to the lack of money, those bandits turned guerrillas were mostly provided with arms, but not sufficient supplies and money.
Split into simpler sentences: The fourth strategic miscalculation made by the retreating nationalist government was financial and economical. These bandits-turned-guerrillas were mostly provided with arms, but due to the Nationalist government's dire financial straits were not given sufficient supplies and money.