Complex sentence: He was the longest-serving head of government of any European Union country, and one of the longest-serving democratically elected leaders in the world, by the time he left office, his tenure encompassing the height of the European financial and sovereign debt crisis.
Split into simpler sentences: He was the longest-serving head of government of any European Union country, and one of the longest-serving democratically elected leaders in the world, by the time he left office. His tenure encompassing the height of the European financial and sovereign debt crisis.