An excellent diplomatic history! One of my weak spots as a historian is US diplomacy btw the Civil War and WWII. I've always understood the individual US conflicts well, but not necessarily the larger strategic architecture of US foreign policy. This book helped me fill in this gaps with its own bold, overarching explanation of USFP.
Mirski starts with the Monroe Doctrine, which is clearly the most important principle of USFP for the nation's 150 years, if not more. During and after the Civil War, successive US presidencies moved to give the Monroe Doctrine teeth, or to move it from a largely aspirational statement of intent to the European powers to something enforceable. US leaders had long wanted the Western hemisphere to be a reserve of republican governments freed from European monarchies. They also wanted to remove European strategic power from the WH to avoid any kind of encirclement of the US.
The main issue with this strategy, Mirski argues, was the problem of order. The United States needed its neighbors to be stable, functional states, preferably at peace with each other, so that there wouldn't be any pretense or opportunity for European powers to insinuate themselves into their affairs. But these were, for a variety of reasons, chronically unstable states, and US leaders doubted their capacity for responsible self-govt for a mix of racial and cultural reasons. So the US ended up interfering more and more in their affairs not out of a grand quest for empire but as part of a strategy of exclusion toward the European powers, of making sure they couldn't take advantage of instability in these countries to regain a foothold in the WH.
This was the strategic vision that drove the creation of US hegemony in the WH. But the means to achieve this evolved over time, pulling the US more and more into the direct management of its Latin American neighbors. Initially, the US supported republican revolutions against European powers, such as the Mexican revolt against France in the 1860s. US leaders sought to foster trade and financial relations with these countries. It seized opportunities to annex or buy territories like Hawaii so that Germans, Japanese, and others would not be able to seize them. This was a strategic necessity in the age of steam, when coaling stations were needed to project global power and protect trade, but they proved But when these defaulted on loans to European partners, fell into civil war, or invaded each other, opportunities arose for European powers to intervene again.
Thus, under TR and Taft, the US ended up acting as the enforcer of international credit, intervening throughout Latin America to collect loans for European and US banks, protecting US property and citizens, tipping the balance toward one government or another in internal disputes, and in cases like Cuba, asserting virtual protectorates. Under the Roosevelt Corollary to the Monroe Doctrine, TR declared a US right to intervene militarily in the Western hemisphere to impose order and keep the Europeans out. Achieving order in the Western hemisphere was a slippery slope that led to dozens of interventions and the souring of relations with Latin American nations, but it was all done with an eye to the global balance of power.
In the 1920, the experience of fighting a bloody insurgency against the Sandinistas in Nicaragua deeply soured the US government against interventionism in the WH, leading to a "good neighbor" approach under FDR that rejected TR's interventionism. But the US never really escaped this problem, and when geopolitical tensions heated up again in the 30s and Germany began intriguing in the WH more, the US turned toward relying on friendly dictators and intervening when necessary. During the Cold War, this problem continued and led to even more US mucking about in Latin America. But, this was undoubtedly a successful strategy that did keep strategic competitors out, ensure US hegemony in the WH, and form the foundation for the global colossus of the Cold War and beyond.
Mirski makes a good argument that while US leaders did have condescending attitudes toward Latin American peoples, but that these attitudes were more facilitators of intervention (and shapers of the nature of that intervention) rather than causes. These attitudes, and grand narratives of manifest destiny or spreading civilization, don't come up much in the primary sources where leaders discuss their reasoning for intervention. First and foremost, US policy in the WH was driven strategic anxiety about locking down this zone of the world from European and other rivals and the fear of what these countries could do if they gained footholds there. This is a good correction to a lot of the literature on US relations with its neighbors that is still compatible with scholarship on race, religion, civilization, modernization, etc. I highly recommend this book!