Complex sentence: In the 1970s, the CJL Foundation campaigned against the proposed Mackenzie Valley Pipeline, which would have sent fossil fuels from the Beaufort Sea to American consumers.
Split into simpler sentences: In the 1970s, the CJL Foundation campaigned about a proposed oil and gas pipeline. The pipeline was to be known as the Mackenzie Valley Pipeline, which would have sent fossil fuels from the Beaufort Sea to American consumers.