Complex sentence: Upon arrival of dictator Ante Pavelić, Zagreb become center of the Main Ustaša Headquarters, NDH government, and other most hostile political and military institutions as well as the police and intelligence services.
Split into simpler sentences: Upon arrival of dictator Ante Pavelić, Zagreb become center of the Main Ustaša Headquarters and NDH government. Zagreb was a seat of the most hostile political and military institutions as well as the police and intelligence services.