Complex sentence: By 1865, the company was operating throughout the Midwest and had made strides along the Eastern Seaboard, prompting the board of trustees to change its name to The Northwestern Mutual Life Insurance Company.
Split into simpler sentences: By 1865, the company was operating throughout the Midwest and had begun entering the market along the Eastern Seaboard. At this time, the board of trustees changed its name to The Northwestern Mutual Life Insurance Company.