Once you have repaired the Embassy, you are now able to earn National Trade Goods by defeating other players in multiplayer battles. You have a chance to earn National Trade Goods for 3-5 star victories, the more stars the greater your chances of earning them. National Trade Goods are kept at your Storehouse, but unlike standard Trade Goods, National Trade Goods cannot be stolen. You can also buy shipments of National Trade Goods at the Storehouse and use them to form War Coalitions at the Embassy. Each Nation has its own National Trade Good as noted below:

Chinese - Tea
British - Timber
French - Cheese
Germans - Salt
Greeks - Scrolls
Japanese - Silk
Koreans - Porcelain
Romans - Marble