Complex sentence: He believed it to be better for Finland if the Social Democrats could be kept outside of the Cabinet, because of which in the presidential election of 1937 the Social Democrats and the Agrarian party voted against him.
Split into simpler sentences: He believed it to be better for Finland if the Social Democrats could be kept outside of the Cabinet. It was due to this that, in the Presidential election of 1937, the Social Democrats and the Agrarian party voted against him.