Complex sentence: Carlos I immediately tried to head off the threat to Portugual's international interests, and he was moderately successful by exercising his considerable diplomatic skills, abetted by family ties to both British and German royalty.
Split into simpler sentences: Carlos I immediately tried to head off the threat to Portugual's international interests. Hewas moderately successful by exercising his considerable diplomatic skills, facilitated by his family ties with both British and German royalty.