Explain diplomacy to me

I haven't actually made an ally yet in 1.3, but here are some things that should improve your relations with a civ:
Send all your trade routes to them.
Research the techs and build the achievements that boost your diplomacy ability.
Boost your military rating by building ships with lots of weapons and using the spin control center.
Choose Good as your alignment if you want to ally with a good or neutral civ.

It is an interesting point. I have not made an ally in my current game either. Bug? The military rating is key with many races. No one wants a weak ally. I am not 100% sure, but I think each race has it's own personal criteria for an ally. There is the obvious alignment, but some like strong offence, some defence. In my current game the Torians instantly became friendly when I met them... I could not explain why though.

As for gifting planets, they're not worth nearly as much as they were in earlier versions, unless you want to trade your entire civilization for one planet of theirs.

I have two allies in my current game. It's with 1.4 though. In 1.3 it is really tough(near impossible)at times to get them close. It may have actually always been this way, but due to the 1.2 and prior bug you could get allied at friendly. I think people just never actually tried for close then, because they didn't need to. As far as who gets close and why, I can't find a logic with it. I've had opposite alignment become close for what seems like no reason, and other times a same alignment civ is impossible to get close. If I plan on alliances, I just kinda take what I can get anymore.

Hi!

Send all your trade routes to them.

Does not help. I have 4 routes (107BC each) to Terrans and only one to Korx (~50BC), but I'm allied with Kors for almost the whole game, and only friendly with Terrans.

Research the techs and build the achievements that boost your diplomacy ability. Boost your military rating by building ships with lots of weapons and using the spin control center. Choose Good as your alignment if you want to ally with a good or neutral civ.

All those help for getting + in relations, but (from my experience) don't help for getting over "friendly". In my current game I'm playing neutral Thalans and am the superpower with ~25 planets (remaining 5 civs have 4-7), have absolute military supremacy (mining 4 mil resources helps somewhat ), have trade routes to every existing civ and overwhelming diplomacy (only Humans are slightly better), but have not been able to make ANY of Terrans, Drath and Iconians above friendly. Then, in next evening after I loaded the game, in just a few turns Iconians went to close. So my advice is: reload the saved game, as this seems to help, when everythiong others fails. And that everything includes giving them ALL one has. Did that in my previous game, to no avail. Arceans just didn't want to get close, so I went after tech victory.

BR, Iztok

I've had two Alliances in my current 3.1 tough game. Maybe it was coincidence but I tried to make lots of trade routes, give away stuff from time to time, traded stuff and have an impressive military.
However, I wasn't able to get a third faction (Alterians) to 'close'. Even when I gave them a planet and they said relations were improved, nothing changed.
To make matters worse, a couple of my fleets were in the area of the planet I gave them, so they got angry and declared war. By that time I was really, really annoyed by them declaring war after I've given them a planet, trade goods, money etc, so I confiscated their empire.
Also, one of my two allies declared war on me because of the assasination event which popped up 300 ships. So I quickly took over a couple of his planets to make him surrender and evaporate his fleet of crappy fighters.
So much for an alliance victory.. Only the Drengin are left as an ally who turned good because of a random event, but are still in the habit of creating scary death fleets of genocide, because that's what there used to.

I think I'll try for alliance in my next game, and then choose good as allignment and try to evade influence techs, because other factions have negative views of factions with too much influence.

I WANT THE ALLIANCE VICTORY, IT HAS THE PRETTIEST END-MOVIE!!!!
(sorry about that)

I don't go for alliances prefering to conquer everyone.

However in my 1.31 suicidal game, I did want to extend the game to the end of the year from early April when I could have won.

I was neutral alignement and left the Yor ( evil alignement ) with 10 planets.
I gave them 2 +39% influence resource starbases.
I also built up a couple of influence starbases by their planets on my border and then gave the starbases to them.
I did that to keep the planets from flipping.

I never had a problem with them the rest of the year and believe they were quite friendly if not willing to ally.( Didn't look all that closely )

I've had two allies since 1.4. The Yor and the Altarians. Both civilizations were faltering early. If an alien civilization gets a solid empire built, you can forget an Alliance. They don't need it, they won't offer it.


What kills me is that I'll see that the AI races have zero problem allying with each other, though.

I've noticed that trading regularly and often helps. One large trade is less effective than several smaller ones. This is harder to do with tech trading off, as there really isn't much else worth trading. You could try gifting things though.

Research all the diplomacy techs. The higher your diplomacy rating compared to theirs, the easier it is to get an alliance. All your trades are worth more as they value what you offer them a lot higher.

All of the answers are pretty much spot on. I find that "gifting" as Evil Muppet stated works wonders in my games. Add a little cash/tech to the mix and you will find some friends. I usually wait until war is going on somewhere and the inevitable help plea comes in... then I see if they're strapped for cash and throw them a bone or two. This is usually enough but I must state that I always play as evil and almost always seek to align myself with the same although I have pulled in one or two neutral/good civs by doing this tactic. Hope it works for you.