Complex sentence: His third wife, Isabel Perón, whom he had married on 15 November 1961, and who had been elected vice-president, succeeded him, thus becoming the first female president in the Western Hemisphere.
Split into simpler sentences: His third wife, Isabel Perón, whom he had married on 15 November 1961, and who had been elected vice-president, succeeded him. She became the first female president in the Western Hemisphere.