Complex sentence: He returned to England in the mid- 1930s only to depart again upon receiving a three-year contract to teach at Peking University, where, upon his arrival, he discovered that due to the Japanese invasion of China, he no longer had available a post.
Split into simpler sentences: He returned to England in the mid- 1930s only to depart again after receiving a three-year contract to teach at Peking University. Upon his arrival, he discovered that due to the Japanese invasion of China, he no longer had available a post.