Complex sentence: After the Second Reform Act of 1867, and the growth of the two-party (Liberal and Conservative) system, the Queen's room for manoeuvre decreased; her freedom to choose which individual should occupy the Premiership was increasingly restricted.
Split into simpler sentences: After the Second Reform Act of 1867, and the growth of the two-party (Liberal and Conservative) system, the Queen's room for manoeuvre decreased. Her freedom to choose which individual should occupy the Premiership (office of the Prime Minister) was increasingly restricted.