Complex sentence: As the leading American diplomat in Vietnam in the transition period between ambassadors, Trueheart refused to take action until he received instructions from Washington, but warned Mau against violating the diplomatic immunity of the USAID offices.
Split into simpler sentences: As the leading American diplomat in Vietnam in the transition between ambassadors, Trueheart refused to take action until he received instructions from Washington. He warned Mau against violating the diplomatic immunity of the USAID offices.