Complex sentence: Since Taiwan does not provide absentee ballots, large numbers of citizens travelled to vote from North America and Mainland China, with typical estimates indicating that about 20,000 people travelled from North America and between 100,000 and 150,000 people travelled from Mainland China.
Split into simpler sentences: Since Taiwan does not provide absentee ballots, large numbers of Taiwanese expatriates living in North America and Mainland China returned to Taiwan to vote. Typical estimates indicate that about 20,000 people travelled from North America and between 100,000 and 150,000 people travelled from Mainland China.