Final answer:
Hugh Gaitskell attempted to amend Clause IV of the Labour Party's constitution, which dealt with nationalization of industry, leading to internal strife and division within the party after their loss in the 1959 general election.
Step-by-step explanation:
After losing the general election in Britain for the second time in 1959, Hugh Gaitskell, leader of the Labour Party, attempted to amend a crucial part of the party's platform which eventually led to significant controversy and division within the party. The clause Gaitskell attempted to amend was Clause IV, which committed the party to the nationalization of industry. This move was perceived as an attempt to move the Labour Party towards the center, away from its traditional socialist policies, and it led to internal party strife and division. Gaitskell believed that this change was necessary in order to make the Labour Party more electable, but it faced strong opposition from the left wing of the party who viewed Clause IV as a fundamental tenet of Labour's identity.