Complex sentence: Burnham, as a "sub-major" firm, needed to connect with a "major" or "special" firm in order to further expand, and found a willing partner in Drexel Firestone, an ailing Philadelphia-based firm with a rich history.
Split into simpler sentences: Burnham, as a "sub-major" firm, needed to connect with a "major" or "special" firm in order to further expand. Burnham found a willing partner in Drexel Firestone, an ailing Philadelphia-based firm with a rich history.