Complex sentence: Spanish explorers arrived in 1536, aboard the "Santiaguillo", a supply ship sent by Diego de Almagro, who is considered the first European explorer, or discoverer, of Chile.
Split into simpler sentences: Spanish explorers arrived in 1536, aboard the "Santiaguillo", a supply ship sent by Diego de Almagro. They are considered the first European explorers, or discoverer, of Chile.