Now these three areas make up all combat. Now you will see how to use them wisely.
Land: Key to conquering anything. You cannot watch carefully over your newly won city from air or sea. You need close up recon. Land units can also destroy a nations economy by destroying bridges, railroad tracks, airports, etc. Tanks, soldiers, and artillery make up this area.
Air: Support for your ground troops. Whether bombing a city for your army to capture or dropping paratroopers for a sneak attack, planes are your main backup units. Bombers are the closest thing you can get to a WMD. Jets can take out the enemy's jets and helicopters. Bombers, fighters, and helicopters make up this area.
Sea: American history shows, port blockades really work. A blockade on major ports will destroy the enemy's economy and many people will starve. Submarines and cruisers can carry a various array of warheads and most ships are also equipped with anti-air guns. Also, aircraft carriers is an air base that you can move from place to place making it a powerful strategic weapon. Destroyers, cruisers, aircraft carriers, submarines, and other ships make up this area.
These are just the basics of modern combat. So study up and you can be a evil genius someday.
Your masterful monarch,
Mr. X