Complex sentence: Relations between the US and its former ally had so deteriorated that this event inspired alarm throughout the government, and people in the military realized that computers would be essential in the defense of the country now that the USSR had the capacity to attack from afar.
Split into simpler sentences: Relations between the US and its former ally had so deteriorated that this event inspired alarm throughout the government. People in the military realized that computers would be essential in the defense of the country now that the USSR had the capacity to attack from afar.