Grammar: westwards or westward?
The form westward is strictly speaking an adjective, such as "westward migration" and westwards is an adverb, so used in constructions such as "the troops continued westwards".
Think of: westward migration (adjective).
Think of: the troops continued westwards (adverb).
About the author
Jesse Karjalainen is the author of The Joy of English: 100 conversations about the English Language, Cannibal – the language and history of the discovery of the New World, and Roanoke – the language and history of Early Colonial America.