Complex sentence: Burnham, as a "sub-major" firm, needed to connect with a "major" 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 at the very least to link up with a "major" firm in order to further expand. They found a willing partner in Drexel Firestone, an ailing Philadelphia-based firm with a rich history.