Bottom-up instead of top-down
You wrote that
I gave them a general history of the planet, a specific history of the continent we started on and specific history of the starting town and surrounding areas.
It seems like you are using a top-down approach. I generally prefer bottom-up. Most people in a fantasy setting will not know anything about the planet or the continent they are living on. Most likely, those concepts will mean nothing to them, or maybe seem like theories for high-level mages or such that do not have any impact on their lives.
Start with only small bits of information on the immediate surroundings of the players, and give them more only if they ask for it, and if it makes sense in the settings that a character would know those things.
Players are interested in backstory if it gets them stuff
In my experience, feeding info dumps to the players is not a successful strategy, as they are usually concerned only with things that affect them and will ignore everything else.
That is, if the information you give them is not about enemies or opportunities for riches, it's often not deemed important. Therefore, try to weave in your information in a way that it relates to those things:
The story of an abandoned tower should contain clues to safely overcome (some of) the traps and other dangers safeguarding the treasure.
The story of a battle fought over the monastery a century ago can be told in the context of the holy avenger sword that was decisive in tipping the odds, but was lost afterwards.
The story of the destruction of the sleepy farming town where the big bad grew up hints to his one true weakness.
Use 4e skill challenges to explore the story interactively
A great way to tell the story is to do it interactively - don't just tell it to them, but let them discover it in a skill challenge. Make sure that they can learn most of the important bits that you want them to learn without rolling, but enrich the story with information on major NPCs, details that give them leverage, or tactical information that they can use to their advantage.
Encourage player to contribute
In a comment, Brian S mentioned another important point - let the players contribute. Allow and encourage them to insert custom elements into the world and fill out blanks that catch their interest. One of the major strengths of pen and paper RPGs is the shared, collaborative approach to story-telling, and integration of player ideas can serve as a great motivator in addition to adding flavour to the world.
Questions
Well, the easiest way is to have your character ask or empathize with other characters in play. "This war has to be pretty hard on you. Weren't you a civilian before?" These work well because they can be a chance to roleplay your character and ask valid questions of theirs.
Some players get stage fright though, so be mindful of that and willing to speak out of character ("Hey, it's cool. I was just hoping to give you a chance to spotlight your character a bit.")
"Remember the time?" loaded questions
This is a fun way, but requires the players to have some trust with each other. You ask loaded questions to them that serves as a starting point, and they take it as true and build off of it.
"Wait, you're not THE 'Nebula-Smasher' Johnson? How DID you escape the Queen's fleet?"
"Is this going to be like the last time you got us BOTH arrested? You still owe me..."
Players who are not good at improv will not roll well with this, and you may want to talk out of character to let people know you might do this.
Scenes and focus of play
This requires the whole group to buy in on it, but it works in a lot of games. "Hey, I'd like to have a scene where I can talk to (fellow PC) about the fallout from these failed negotiations. Can we do that?"
Openly requesting and declaring scenes makes it really easy and fun to set up scenes about beliefs, personality, history, and thoughts on the situation. It lets everyone know what you're interested in, and to spend time exploring characters specifically.
Best Answer
Show them. :) It's always best to lead by example. Have your Non-player characters use specific references and attitudes that can be easily copied -- however clumsily at first! -- and keep on hammering them with good examples until they get the hang of it.
If and when players lapse into American-speak or other characteristics you don't want to encourage, again rely on your NPCs. Have them misunderstand, react poorly to innocent comments, and provide other negative reinforcement (tho as little as necessary) to illustrate the worst-case scenario.
As noted in other responses here, reward it when they try. Keep the rewards small at first, but specify clearly exactly how much they're getting for which comments, attitudes, and actions. Then increase the rewards in response to more and better attempts. Next thing you know you'll have started a trend... and the better players of such roles will be getting bigger and better rewards. They'll keep leading by example, taking a lot of the load off your shoulders.
Finally, find written works (if you can) that can supply both ideas and one-liners that can be used or copied by the players. Such things will vary widely by setting and culture, else I'd recommend specific examples.
Best of luck!