Complex sentence: Although the Mariel boatlift was partially a Cuban response to Western failure to take the dissidents out of Cuba, it was sparked by the removal of the Cuban security guards from the Embassy of Peru compound resulting in its being overrun by thousands of Cuban asylum seekers.
Split into simpler sentences: Although the Mariel boatlift was partially a Cuban response to Western failure to take the dissidents out of Cuba. It was sparked by the removal of the Cuban security guards from the Embassy of Peru compound resulting in its being overrun by Cuban asylum seekers.