Complex sentence: The two left the Multics project when Bell Labs withdrew from it, but they used the experience from the project, and in 1969, Thompson and Ritchie became the principal creators of the Unix operating system.
Split into simpler sentences: The two left the Multics project when Bell Labs withdrew from it, but they used the experience from the project. In 1969, Thompson and Ritchie became the principal creators of the Unix operating system.