Not all Articles of Agreement in the game can be received for free. The thing is that you may receive only basic Articles of Agreement for entering the game every day. Once you sign all the basic Agreements, you will start receiving a 7% bonus to your Timber and Bronze production rates.
You may check whether you are already receiving that bonus on the right side of the Agreements window.
Once the bonus unlocks, it will mean that you have only special Agreements left to negotiate. These Agreements unlock Roman units. Parts for such Agreements can be purchased for GP's, at the Market, or through the Agreements window itself.
The GP's are extremely rare and valuable, so the only way to earn them is to compete in Tournaments.