The ultimate in globalization would be a world in which "the economic system as a whole" is not a national economy but the world economy, and in which no one nation could affect "the system as a whole." Perhaps that time has come already.
The prescriptions of macroeconomics would then have to be addressed to the community of nations throughout the world. In order to solve macroeconomic problems, we would first have to solve the political problem of coordinating macroeconomic policy among the major nations. That's pretty frightening. Nations have been working on that for several decades, and the political problem still seems very difficult. Complex as economics is, there are other things that seem to be more complex.