Complex sentence: Anstey was one of the few Labor members who opposed the war from the start, and was for a time highly unpopular as a result, but by 1917 antiwar sentiment was growing and Anstey became one of the leaders of the movement against conscription for the war.
Split into simpler sentences: Anstey was one of the few Labor members who opposed the war from the start, and as a result he was highly unpopular for a time. By 1917, however, anti-war sentiment was growing and Anstey became one of the leaders of the movement against conscription for the war.