In a few situations, you can send your Stealth Bombers to plummet an enemy city's HP and send your unique infantry to secure and guard the captured city. This process can be repeated many times as possible as long as you assimilate and repair occupied cities.
Remember that your first Wonder is constructed instantly so be sure to build a Wonder that boosts your economy or takes a long time to construct. One especially beneficial wonder to construct is the Terra Cotta Army. This wonder provides one free light infantry every 30 seconds (which are unique units with automatic self entrenchment for Americans) thus boosting defense. The infantry so created provides free resources (American specialty), thus boosting the economy as well.