Complex sentence: He joined a group of mainly Birmingham based MP's, led by Joseph Chamberlain, who disagreed with William Gladstone on a number of issues, particularly his Irish policies, and had created the Liberal Unionists in 1886.
Split into simpler sentences: He joined a group of mainly Birmingham based MP's, led by Joseph Chamberlain. These MPs disagreed with William Gladstone on a number of issues, particularly his Irish policies, and had created the Liberal Unionists in 1886.