Complex sentence: Mendelevitch has been a political activist from his days in the former USSR, when he moved to Israel and as globetrotting speaker on behalf of various causes, such as lobbying for the release of convicted spy Jonathan Pollard in the USA.
Split into simpler sentences: Mendelevitch has been a political activist from his days in the former USSR. When he moved to Israel, he became a globetrotting speaker on behalf of various causes, such as lobbying for the release of convicted spy Jonathan Pollard in the USA.