“…The authors recommend supporting U.S allies through both active diplomacy and the stationing of military forces in or near potential conflict zones. America’s global network of alliances fulfills “the main imperative of U.S. grand strategy,” as the authors describe it: “to prevent the emergence of a power or combination of powers within the Eurasian landmass that could invade or economically dominate the United States.” Alliances are an inexpensive alternative to direct containment through the maintenance of large U.S. forces overseas or to a retreat from such commitments that could result in a costly re-entry if a rival becomes a grave threat. The authors remind us that “strengthening American military competitiveness against a large power in its own region has been the organizing purpose for the United States to form defensive alliances….”
https://www.wsj.com/articles/probing-for-weakness-1458775212