Complex sentence: From 1943 to 1945, racing was not held at Saratoga Race Course due to travel restrictions brought on by World War II; in those years, the stakes races that would have been run at Saratoga Race Course were contested at Belmont Park instead.
Split into simpler sentences: From 1943 to 1945, racing was not held at Saratoga Race Course due to travel restrictions during the war. During those years, the stakes races that would have been run at Saratoga Race Course were contested at Belmont Park instead.