1. Introduction of the game:
Game of War - Fire Age is an enthralling mobile strategy game that invites players into a world of mythical conquest and empire building. Developed by Machine Zone, Inc. (now known as MZ), it is a real-time massively multiplayer online game that challenges players to build mighty empires, forge alliances, and battle against players from around the globe.

2. All characters and levels of the game:
While Game of War doesn't follow a traditional character-based format, players assume the role of a city leader and strategist. There are various levels in the game which correspond to the player’s city development and military strength. Progression includes constructing and upgrading buildings, training armies, researching technologies, and leveling up the hero who leads your armies in battle.

3. What attracts users most to the game:
Users are most attracted to Game of War's extensive social interaction, which includes forming alliances with players worldwide and engaging in diplomacy or war. The game's real-time translation of chat messages breaks down language barriers and enables a more inclusive gaming experience, making it highly engaging for a diverse audience.

4. Why it is popular:
Game of War - Fire Age gained significant popularity due to its extensive marketing campaigns featuring celebrity endorsements. Its popularity is also rooted in the game's addictive gameplay loop, its competitive nature, and the social dynamics that encourage players to spend considerable time building and defending their empires, and forming strategic alliances.

5. When the game was released and how many versions are currently available:
Game of War - Fire Age was released on July 25, 2013. The game has seen numerous updates and expansions since its release, but it is considered a singular evolving title rather than having distinct "versions" in the traditional sense. As it is regularly updated for balance and content, it stays relevant to the player base with new features being frequently added.

6. The most difficult part of the game:
The most challenging aspect of Game of War is often the late-game content where players must strategically coordinate with alliance members and utilize a deep understanding of the game mechanics to successfully compete against well-established and powerful opponents.

7. Strengths and weaknesses of the game:
Strengths include the game's deep strategy elements, the social aspects, and the continuously updated content which keeps the game fresh. However, its weaknesses often cited by players include a pay-to-win model that heavily favors players who are willing to spend real money on in-game advantages and a sometimes overwhelming complexity for new players.

8. What other games have been developed by the same developer:
MZ, the developer of Game of War - Fire Age, is also known for developing similar genre titles such as Mobile Strike, a modern warfare strategy game, and Final Fantasy XV: A New Empire, which is a strategy game based on the popular Final Fantasy universe. These games also emphasize multiplayer alliances and strategic gameplay.