Complex sentence: Congress had passed acts promising land grants to the first railroad to reach the Kansas border via the Neosho Valley and the part of the Katy had been the Union Pacific Railway, Southern Branch was in a heated competition for the prize.
Split into simpler sentences: Congress had passed acts promising land grants to the first railroad to reach the Kansas border via the Neosho Valley. The Katy portion of the former Union Pacific Railway, Southern Branch was in a heated competition for the prize.