Complex sentence: From 1885 to 1890, he spent time in London, where he became a close friend of Friedrich Engels; in 1891, he co-authored the SPD's Erfurter Programm together with August Bebel and Eduard Bernstein.
Split into simpler sentences: From 1885 to 1890, he spent time in London, where he became a close friend of Friedrich Engels. In 1891, he co-authored the Social Democratic Party of Germany (SPD) 's Erfurt Program together with August Bebel and Eduard Bernstein.