With any city-builder comes a constant battle for space, and even though Zynga's newest Facebook game Empires & Allies is about far more than the city-building portions, you'll still spend the majority of your time back on your Home Island(s) creating new military units, refining oil, processing wood and so on. You'll need space to build more and more buildings as you level up, and you'll eventually need to expand your land.
Players of CityVille will recognize the system here. Currently, your very first expansion comes at a price of 5,000 coins and 10 Liberty Bonds. Liberty Bonds are the equivalent of CityVille's Zoning Permits, and you'll need to collect them from friends in mass quantities to expand each and every time you do so. There's a catch here though. Whether by some oversight or intentional design choice, you can't currently ask for Liberty Bonds via the game's expansion menu (found in the game's store - the Hard Hat icon). Only when you've earned enough coins to purchase the expansion will you be able to ask for Liberty Bonds, forcing you to wait quite a while instead of accomplishing two tasks at once.
Either way, you can work around this and expand early, if you put your mind to it. Participate in battles frequently, and you'll receive Liberty Bonds as prizes. Furthermore, Liberty Bonds are currently available to send via the game's free gifts page, so your friends can send you as many (or as few, if you don't remind them) as they'd like.