Complex sentence: By 1981, Santos had mostly retired from political life, devoting his activity to veterans affairs; thus, it came as a surprise when he agreed to run for President against Ferdinand Marcos in the 1981 elections.
Split into simpler sentences: By 1981, Santos had mostly retired from political life, devoting his activity to veteran's affairs. It came as a surprise when he agreed to run for President against Ferdinand Marcos in the 1981 elections.