Complex sentence: In the 20th century, the USSR represented themselves as the foremost enemy of imperialism, and thus politically and materially supported Third World revolutionary organisations who fought for national independence; as such the USSR sent military advisors to Ethiopia, Angola, Egypt, and Afghanistan.
Split into simpler sentences: In the 20th century, the USSR represented themselves as the foremost enemy of imperialism, and thus politically and materially supported Third World revolutionary organisations who fought for national independence. The USSR sent military advisors to Ethiopia, Angola, Egypt, and Afghanistan.