You can press the 'Abdicate' button in the 'Options' tab to convert your Coins, buildings, and upgrades into Gems if you decide you want to restart the game again. Doing this will boost the your next session's overall production. Also, any Trophies and some stats will be saved and carried over to the new session which will result in better bonuses. Note: Faction alliances will be reset when you abdicate allowing you to switch alignments and affiliations.