The thing that would stand out to me about that line is that he calls the us 'The western sector of America'.
If the distinction here is between North and South America, it's seems extremely illogical to label it 'western'. Actually almost seems to imply that the US no longer controls the entire eastern part of North America.
West and Far West are employed globally to speak of the regions west of the Mississippi without complete regard to political borders. It is primarily known for geography: plains, mountain ranges, lack of rivers and aridity. Spock could use it without implying that the US does or does not exist.