Original: The Second War of Scottish Independence began properly in 1333 when Edward III of England overturned the 1328 Treaty of Northampton, under which England recognised the legitimacy of the dynasty established by Robert Bruce.
Simplified: The Second War of Scottish Independence began in 1333 when Edward III of England did not accept the 1328 Treaty of Northampton any more, under which England recognised the legitimacy of the dynasty established by Robert Bruce.