One day, humanity may receive a signal from the vast reaches of Space that will undeniably confirm that we are not alone in the sea full of stars. Should that happen, it’s say to assume that a lot of resources will be put into finding the origins of that signal with humanity striving to explore the point of origin over the years ahead. Reversing that situation, where the early attempts by humanity to reach out to possible alien races are found, they’re going to come looking to see who sent the message, and what they want.
This takes us to the events of Battleship, where an alien species does come looking for the point of origin, discovering a planet full of life but still in its space age infancy. All goes well until some of the satellites around the planet cause damage to the alien ships, causing thm to come crashing down to Earth, no doubt putting those on board in a state of some panic. After all, you’re about to crash onto an uncharted world with no idea how the inhabitants will respond, not to mentioin that your communications ship is the first casualty as it crashes into a settlement, killing those on board as well some of the city dwellers.
The rest of your exploration fleet manages to group together and get a softer landing, but this has obviously drawn the attention of the planet’s defence forces. One of the indigenous creatures approaches one of your downed vessels, but without knowing its intentions the order is given to create a force field, trapping both yourselves, and representatives of Earth’s forces so discussions can take place. If you can explain the accident and work with these humans to retrieve the communications ship then maybe things can be smoothed over.
The Earth ships send out a message via a horn and the aliens respond in kind. Dialogue is taking place, but almost immediately the Earth forces start firing their weapons. Remember, even though these alien ships have crashed and caused casualties, there has been no evidence of actual hostilities, plus there are probably wounded aliens on the ships. The Navy is firing upon ships that would require help, not further damage.
As one of the commanding officers on an alien ship it is the duty to protect those on board, and the only real way to do that is eliminate the now present threat. You change the status of the human ships from friendly to foe, which gives clearance to respond with your own weapons. The aliens destroy some of the human ships and, to show you’re not fooling around, you also hit the nearest settlement. As soon as the alien ship was fired upon, war was declared.
But now you’re engaged in a war with an extremely hostile species on their own territory, so you have to act fast. You know the signal your ships received were sent from a nearby location, so it makes sense to find the place and send your own SOS. The alien scouts discover a mass satellite array on the land nearby, sending a team to secure and modify the structure to call for reinforcements, or a rescue mission to get off Earth.
In the reports that are sent back it must be made clear that a species so dangerous, and on the brink of discovering how to travel the vast distances of the galaxy quickly, must be stopped. After all, they fired on a wounded neutral ship, so what are they like when they hate something? It’s critical that the galaxy is made aware of the threat, even though it’s likely the alien commander won’t see the result of the message.
However, time is against the aliens as the satellites need repositioning and the process will take hours, so the only thing that can be done is to hold off the aggressive inhabitants. But with crippled ships that can only be done for so long, and the humans know this, eventually piercing the defences of the alien ships, destroying them one by one. In those final moments the alien commander knows his mission has failed and that his people won’t know the threat that awaits them should they come to investigate in their wake.
The aliens will come looking for their missing ships, and they’ll probably work out something went horribly wrong. All that can be done is send another scouting party to find the missing crews, and determine the facts. However, when the scouting parties get to the final point of contact they won’t like what they see, and the war will likely escalate, unless the communications barrier is broken between the two races. The next time, the humans will not win against a large scale invasion fleet seeking revenge.