Complex sentence: Other northern states would be taken from U.S. control as well, specifically Oklahoma, Wyoming, Kansas, Nebraska, South Dakota, and Utah, and they would be used to create an independent buffer state, further separating the United States from Mexico.
Split into simpler sentences: Other northern states, specifically Oklahoma, Wyoming, Kansas, Nebraska, South Dakota, and Utah, would be taken from U.S. control as well. These northern states would be used to create a consolidated and independent buffer state to further separate the United States from Mexico.