CANT WIN, WHY???

Ryan,

Do a search on the forum using Alliance as the keyword. You will find threads describing the prerequistes for allying.

I'm just going to say the big requirements. Just because your military can beat them doen't mean they'll ally with you. First you need the Alliance technology. Then you also need your relations to be Close. If both of these are true the option to make an alliance will be there but might have to give them a few ships or something.

~SDC~

To add to what Ray and Geoffrey said, I believe both you and the Arceans need alliance technology. However, if they don't have it, you can always give it to them. That has the added bonus of improving your relations.

To add to all the previous:
Under their pictures in the relations screen you have a slider which shows the level of your relations with them. It helps to determine if they're almost ready to be your ally (and a gift of some sort should suffice) or if you still need to work on your relations with them, by orienting your trade towards them (or developping techs that allow you to have new trade routes). This will bring them to close in time, and them you can ally.

First of all to ally with some one. A good idea is to declare war on a civilization that the civilizations is at war with example:
I declared war on the Yor Collective becaus the Arcean Empire was at war with them too.
Then give them like 1,000 bc and 3 techs they don't have
The last and most important thing you need to research these:
Phasers, Instant Communication, Alliances.

Then once it comes on you're screen offer and alliance.

Cheers,
Malaphar