Complex sentence: The decision was preceded by one day in Gospić, when the Croatian forces when a JNA storage facility was captured on 13 September--providing the Croatian troops with 14,000 rifles and a substantial quantity of antitank weapons.
Split into simpler sentences: The decision was preceded by one day in Gospić, when the Croatian forces captured a JNA storage facility on 13 September. This provided the Croatian troops with 14,000 rifles and a substantial quantity of antitank weapons.