Complex sentence: Wartime is not the only circumstance of significant numbers of military deaths, constantly training and preparing for war also involves significant dangers, peacetime military accidents claim lives every year at a significantly higher rate than accidents for the civilian population.
Split into simpler sentences: Wartime is not the only circumstance of significant numbers of military deaths. Military service can also be dangerous in peacetime and military accidents claim lives every year at a rate significantly higher than the civilian population.