Complex sentence: This impression was reinforced by buffer zones established by the JNA after fighting between Croatian Serb militia and the ZNG--the JNA often intervened after the ZNG had lost territory, leaving the Croatian Serbs in control of areas they had captured before the JNA stepped in.
Split into simpler sentences: This impression was reinforced by buffer zones established by the JNA after fighting between Croatian Serb militia and the ZNG. The JNA often intervened after the ZNG had lost territory, leaving the Croatian Serbs in control of areas they had captured before the JNA stepped in.