Complex sentence: His daughter, Margaret, married the Scottish king in 1502, which was expected to bring about perpetual peace between the two countries and which might have been the outcome had the Scots given up theirAuld Alliance with France.
Split into simpler sentences: His daughter, Margaret, married the Scottish king in 1502, an alliance expected to establish perpetual peace between the two countries. That might have been the fortunate outcome had the Scots given up their Auld Alliance with France.