Complex sentence: Before the war, the Kingdom of Romania was an ally of Austria-Hungary; however, when war broke out in 1914 Romania pledged neutrality-claiming that Austria-Hungary had started the war and thus Romania had no obligation to join it.
Split into simpler sentences: Before the war, the Kingdom of Romania was an ally of Austria-Hungary. However, when war broke out in 1914, Romania pledged neutrality, claiming that Austria-Hungary had started the war and thus Romania had no obligation to join it.