The military power of New America is definitely not sufficient to both secure the rear and have enough strength to intervene in Night City. If it were, they could have launched an attack two years ago when Arasaka withdrew from Night City!
Although there's no detailed data, Lille fully understands Miles's current predicament:
After a warlord captures a city, the resources consumed to maintain order and enforce willpower could completely exceed those used in war!
In war, you can choose whether to pour resources into capturing strategic points, but occupation is different. If Miles decides to abandon those uncontrollable cities, either by bloody measures or simply giving up, all resources invested would become sunk costs, potentially even disrupting the expected economic output, which is unacceptable!
However, man proposes, God disposes. Now that the Euro has completely collapsed, the global financial system has fallen into semi-paralysis due to the European civil war——
