Complex sentence: The global financial crisis of 2008, which was considered by many to be the worst financial crisis our world has seen since 1929's Black Thursday, had left France and the rest of Europe exhausted and indebted.
Split into simpler sentences: The global financial crisis of 2008 is considered by many to be the worst financial crisis our world has seen since 1929's Black Thursday. It had left France and the rest of Europe exhausted and indebted.