I have a space game idea that takes place in 1 stellar system. The idea is that there are no faster than light travel engine, so traveling from a system to another takes dozens of years. So players are trapped in the same stellar system and they must colonize and conquer planets.
I want the game to end after a certain number of turns which could not be fixed. For example, I could have an end game like dungeon quest, where you could get a few extra turns if you are lucky. When the game ends, the player with the most VP wins.
But the problem is: Why would the game end? What is happening at the end of turn X for the game to be over?
I am lacking of ideas, the only idea so far is that there could be a colony ship on it's way and the faction who did the best will be colonized in priority when it arrives. Each turn would be a year, so if a ship takes a dozen of years (turns) it could be logical.
Anybody else have an idea?
Thank for the comments. I made a mirror thread on BGG and got similar reply. A few details I forgot to mention:
The player has just arrived in the system where the game takes place, so I did not want to use a mechanic where the system self destruct or is under attack as end game condition.
For alien attacks, I might include them in the regular game like the barbarians in "settlers of catan" where players must collectively commit a certain number of ship to repel the invasion.
There seems to be 2 options either the system is waiting for something to arrive, like suggested by myself and another person.
Or the other solution posted on BGG is that the players must build another colony ship to colonize another system to repeat the process they just did. So the first player to build the ship, accumulate the fuel and have the population requirements for the ship wins the game.