Complex sentence: The Liberals, who by ideology and history were strongly in favour of free trade, decided to make the issue the central plank of their re-election strategy, and negotiated a free trade agreement in natural products with the United States.
Split into simpler sentences: The Liberals, who by ideology and history were strongly in favour of free trade decided to make the issue the central plank of their reelection strategy. Thus a free trade agreement in natural products was negotiated with the United States.