Complex sentence: The National Bank of Detroit (NBD) was a bank that operated mostly in the midwestern United States until it was purchaced by First Chicago in the mid- 1990s; the combined bank was called First Chicago NBD, but bank branches remained under the NBD name.
Split into simpler sentences: The National Bank of Detroit (NBD) was a bank that operated mostly in the Midwestern United States. It was purchaced by First Chicago in the mid- 1990s; the combined bank was called First Chicago NBD, but bank branches remained under the NBD name.