With the launch of Battle Nations on iOS, developer Z2Live is hoping to repeat the success that has made it a force in the free-to-play games market.

Seattle-based Z2Live might not be as well-known as other mobile developers like Angry Birds maker Rovio, but the studio’s first two games — Trade Nations and Metalstorm: Online — can regularly be found near the top of the highest-grossing app charts on iOS (iPod, iPhone, iPad). Now the developer is following that up with the recent launch of Battle Nations. As it does so, the company is finding ways to stand out in a sea of mobile game developers. That’s increasingly hard to do.

Whereas its previous games focused on vastly different markets — Trade Nations is a social city-building game while Metalstorm is a 3D air-combat game — Z2Live’s latest game is somewhat of a blend of the two, letting players build up a military city and engage in strategic combat with both other players and computer controlled armies.

The idea behind the game was actually inspired by feedback from players.

“Players have consistently wanted to attack their neighbors,” Z2Live chief operating officer Lou Fasulo told VentureBeat, “but this didn’t feel like the right game play expansion for Trade Nations so we decided to build an entire new title around the concept. This also created an opportunity for us to put our learnings from Trade Nations to work in a new title.”

He added, “Our experience with Metalstorm also contributed both technologies and design best practices. Specifically, Metalstorm taught us a lot about the relative importance of player-versus-player and single player content. It also provided some of the underlying technology for the Battle Nations battle system. You can’t see it as a player, but when you engage other players in Battle Nations random PvP matches, Metalstorm’s match making technology is under the hood.”

The name of the game was also influenced by past releases, attempting to create a recognized brand based on the success of Trade Nations.

While many mobile developers are content with a rapid release schedule, launching new games with very short development cycles, Z2Live has gone a different route. Three games in three years is quite slow by mobile standards. Part of this has to do with the company’s origins. Prior to the release of Apple’s Game Center app, Z2Live was attempting to build something similar to offer users an Xbox-live style experience on a mobile device. It received $3 million in funding for the idea in August 2009. Once Apple entered the ring Fasulo and his team decided to shift their focus and work in internally developed games.

As the studio continues to grow Fasulo says that the rate at which new games will launch will increase, but that the developer will still maintain a focus on quality game experiences.

“We don’t have ambitions to release a new title every month,” he said, “we would rather build brands that players can engage with for years to come. Trade Nations is a perfect example: we have players that have been with the game, and with Z2Live, for over a year and they continue to look forward to each new release of content and expansion of the universe.”

Battle Nations, as with all of Z2Live’s mobile games, is free to download but monetized via in-app purchases. In Trade Nations, for instance, users can purchase a premium currency called “magic beans” that can be used to buy special in-game items or speed up the production of resources. Battle Nations uses a currency called “nanopods” that can be used in much the same way. For Z2Live, the free-to-play model is useful in reaching as many players as possible.

“We’re big believers in the value of having a large player base,” Fasulo said. “Specifically in social games, where interaction with friends and other players is a big part of the engagement. Having said that, not all gameplay models make sense in the freemium format. It’s easy to see why freemium is becoming popular, but unfortunately, not everyone understands how it works or when its appropriate. There will be some painful learning – freemium is not a panacea; games will always be about creating that engaging moment-to-moment fun experience.”

The developer is currently in the midst of fixing bugs for the newly launched Battle Nations and making changes based on player feedback. After that the focus will be put on to developing the second chapter of the story arc and adding more features to the player-versus-player multiplayer portion of the game.

“The feedback from players has been overwhelmingly positive, so we’re very excited about the future of the game.”