Meshech was a Japhethite territory far to the north of Canaan. Kedar was an Ishmaelite territory in Arabia. Violent people lived in both places.
Meshech was known for its slave trade (Ezekiel 27:13; see also Exodus 21:16), and Kedar was known for its warriors (Isaiah 21:16–17). These places represented the rebellious and violent land where the psalmist suffered.