Complex sentence: Later, however, he expressed ambivalence about becoming America's most notorious tax resister and wrote that his act of civil disobedience could have effected dramatic reforms in tax law had 10 or 20 million of his fellow Americans joined him in defying the IRS.
Split into simpler sentences: Later, however, he expressed ambivalence about becoming America's most notorious tax resister. He later wrote that his act of civil disobedience could have effected dramatic reforms in tax law had 10 or 20 million of his fellow Americans joined him in defying the IRS.