Grammar: northwards or northward?
The form northward is strictly speaking an adjective, such as "northward migration" and northwards is an adverb, so used in constructions such as "the troops continued northwards".
Think of: northward migration (adjective).
Think of: the troops continued northwards (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.