Complex sentence: Original models, powered by engines from Fordson tractors were drawn by horses or tractors and by the late 1940s and early 1950s, self-driving or self-propelled combines were introduced by various farm equipment manufacturers.
Split into simpler sentences: Original models, powered by engines from Fordson tractors were initially drawn by horses or tractors. By the late 1940s and early 1950s, self-driving or self-propelled combines were introduced by various farm equipment manufacturers.