Relation means the fact that two things are related.
Relationship means how they are related.
E.g. Wrong example: Our relation is father and son.
Correct example: Our relationship is father and son.
The word Relation is seldom used. Usually, we say \"these two things are
related\" instead of \"these two things are in relation\".
**** another example:
Wrong: The relation between Japan and China is getting worse.
Correct: The relationship between Japan and China is getting worse.