Complex sentence: RCA licensed a competing tube to many of the same manufacturers, with a clause requiring the licensee to only buy from RCA, causing a significant decline in Raytheon's market share over the next few years.
Split into simpler sentences: RCA licensed a competing tube to many of the same manufacturers, with a clause requiring the licensee to only buy from RCA. This clause caused a significant decline in Raytheon's market share over the next few years.