Disasters are inevitable in Sim City. No matter how well your little town is managed, it will invariably fall prey to occurrences such as earthquakes, flood, and alien invasion. Finally, you can fight back.
A few years after an alien spaceship unleashes destruction, an announcement makes the headlines.
"After years of working in secrecy, Halfbakersville's top scientists have unlocked the alien invader's secret of interstellar travel. Their home world has been located. The city eagerly awaits the mayor's plan of action."
The player is then presented with the choice of whether or not to launch a counterattack. Accepting is costly, and requires a certain level of infrastructure, but immediately elevates the mayoral approval rating. After all, memories are still fresh, and what citizen doesn't have a little bloodlust? A fleet of ships is launched, with much fanfare throughout the city.
Then, you wait. And wait some more. A century; maybe even two or three. Stardrives may be fast, but space is vast. The mission quickly slips from the public mind, and soon is only found in history books. In the meantime, land doesn't rezone itself: you must return to your mayoral duties.
Suddenly, the news hits the papers. "Space Hero Returns to Halfbakersville! The sole time-dilated survivor of a 250 year old extraterrestrial counterstrike arrives with a tale of impending doom: the aliens are returning." As acting omnipotent mayor, you face the important decision of how to defend your constituents.
Anti-spacecraft laser defense turrets may be constructed, but are costly in terms of money, electricity, and cooling water. Public support is initially high, but it seems the alien foe has taken the scenic route through the galaxy.
As time passes, initiatives dwindle. With nary a UFO sighting in generations, patriotism fades. Citizens balk at the cost. Wildlife conservationists complain of accidental Bull Moose zappings. The rich scoff at ugly embankments in the neighbourhood; surely the aliens aren't going to invade *their* backyard. The turrets may be demolished to appease these naysayers, at the risk of leaving the city defenseless.
Eventually, the aliens return. Their craft will soon be eliminated if enough turrets are present. If not, the destructive force will go unchecked, reducing entire blocks to rubble in seconds. Trying to build new turrets in the middle of an invasion goes about as well as one could hope. Eventually, the attackers leave.
The populous--or what's left of it--will of course be shocked to know the aliens were real. Greater defenses will be demanded, as will another strike force. They vow never to forget the importance of the laser turrets. Their children's grandchildren however might not be so understanding in a couple hundred years.