Complex sentence: Financial difficulties in the early 1870s forced the Northern Pacific to sell off much of its lands in the upper Midwest, which brought Tower into possession of large tracts of land in Minnesota, North Dakota, and Washington.
Split into simpler sentences: Financial difficulties in the early 1870s forced the Northern Pacific to sell off much of its lands in the upper Midwest. Tower acquired large tracts of land from the sales in Minnesota, North Dakota, and Washington.