The next significant change for C&O came in 1923 when the great Cleveland financiers, the Van Sweringen brothers (O. P. and M. J. Van Sweringen), bought a controlling interest in the line as part of their expansion of the Nickel Plate Road (NKP) system. Eventually they controlled the NKP, C&O, Pere Marquette Railroad (in Michigan and Ontario), and Erie railroads. They managed to control this huge (for the time) system by a maze of holding companies and interlocking directorships. This house of cards tumbled when the Great Depression began and the Van Sweringen companies collapsed.