Complex sentence: Cabotage by merchant ships is prohibited in most countries that have a coastline so as to protect the domestic shipping industry from foreign competition, preserve domestically-owned shipping infrastructure for national security purposes, and ensure safety in congested territorial waters.
Split into simpler sentences: Cabotage by merchant ships is prohibited in most countries that have a coastline. Such policies are intended to protect the domestic shipping industry from foreign competition, preserve domestically-owned shipping infrastructure for national security purposes, and ensure safety in congested territorial waters.