Complex sentence: He served as a legal adviser for the United States Defense Department (to which he was appointed by Henry Kissinger) and as the Legal Adviser of the Department of State, NATO mission envoy, and president of the American Society of International Law.
Split into simpler sentences: He served as a legal adviser for the United States Defense Department and was picked by Henry Kissinger to serve as Legal Adviser of the Department of State. He was also NATO mission envoy, and president of the American Society of International Law.