Step 1: Understanding the Question:
The question has two distinct parts: the reason for Dr. Sadao's education in America, and the reason he was not sent abroad with the troops during the war.
Step 2: Detailed Explanation:
Dr. Sadao was sent to America at the age of twenty-two by his father, who was a stern patriot but believed in modern education. The sole purpose was for Sadao to become a highly skilled and famous surgeon. Later, during the war, Sadao was not sent to the battlefield with other doctors. He was kept in Japan for two reasons: firstly, he was perfecting a discovery to render wounds completely clean, and more importantly, the old General was critically ill and might require surgery at any moment, and he had absolute faith only in Dr. Sadao's abilities.