Complex sentence: However, the mainframe computer market was dominated by IBM-other companies could not deploy resources for development, customer support and marketing that IBM could use, making competition in this segment difficult after the introduction of the IBM 360 family.
Split into simpler sentences: However, the mainframe computer market was dominated by IBM. Other companies could not deploy resources for development, customer support and marketing on the scale that IBM could afford, making competition in this segment difficult after the introduction of the IBM 360 family.