Complex sentence: At the time the embargo was imposed, only the Yugoslav National Army (JNA), which was believed to be neutral, had significant supplies of heavy weapons; however, as the conflict progressed the Army fell under Serb control.
Split into simpler sentences: At the time the embargo was imposed, only the Yugoslav National Army (JNA), which was believed to be neutral, had significant supplies of heavy weapons. However, as the conflict progressed the Army fell under Serb control.