Complex sentence: By 1950 most had been sent, willing or not, to Hokkaidō, though they had to leave all of their possessions behind, including any currency they had, Russian or Japanese, so they arrived on the Japanese home islands penniless and homeless.
Split into simpler sentences: By 1950 most had been sent, willing or not, to Hokkaidō, though they had to leave all of their possessions behind. They also had to leave behind any currency they had, Russian or Japanese, so arrived on the Japanese home islands penniless and homeless.