The biggest change discards a rule introduced in Civilization V: one unit per tile. While you could technically place military units together with civilian ones, you will now be able to combine many units for combat bonuses or protection reasons. This will get rid of some serious pain points from earlier games, but also introduce new tactical elements.

Early in a Civilization V campaign, for example, you had to flank a settler unit with warriors, or hope barbarians did not capture them. Likewise, workers building roads out in the open were a big risk, and you had to keep on moving a warrior along with them. Now, you'll simply be able to combine a settler or worker unit with a warrior unit to ensure they can't randomly be jumped. Later on in the game cycle, you'll be able to combine different military units to create better-rounded armies. Think about combining an anti-tank unit with an infantry unit to cover one another's weaknesses. You could also combine two units of the same type for a new ultra-powerful "Corps" unit. This will seriously change the way combat works. While older Civ titles let you stack units on a single tile, they did not act as a single unit as they will in Civilization VI.

In another shake-up, the way cities expand is changing. In previous Civ games, a city itself took up a single tile, with only the land borders around it expanding. Now, cities will physically expand to consume tiles around them. You'll be able to plan out the layout of each settlement, making individual cities more unique -- a military city might have a very different layout to a farming town. You'll have to craft cities based on the terrain around them to take full advantage of nearby resources.

Diplomacy and Research are also seeing an overhaul. Your conversations with other leaders will change significantly depending on which age -- stone, bronze, etc. -- you're in. This makes a ton of sense compared to the static diplomacy of the past. Expect primitive interactions in early game, and more conflict and war, to give way to complex alliances and negotiations as your society progresses. For Research, you'll now be encouraged to explore new lands and develop the local environment. Doing so will unlock boosts that advance the speed topics are researched.

Finally (for now, at least), there are tweaks coming to accessibility and multiplayer. While the game is designed for long-time Civ fans, a fresh tutorial system is promised that will ease new players slowly into the myriad aspects of a campaign. For multiplayer, a new mode is coming based around scenarios. This as-yet unnamed mode can be played both cooperatively and competitively, and is designed to be "easily completed in a single session."

Expect to hear a lot more about Civilization VI soon. The game is scheduled for release on October 21st. Previous titles have also come to OS X and Linux, but as of now it's only confirmed for PC. We're likely to learn about new features, tweaks and release plans for additional platforms over the coming weeks months leading up to the launch.

Correction: This article has been modified since publishing to better explain the way unit combination will work in Civilization VI. It previously stated that having more that one unit per tile was new to the series. While unit combination is a new feature addition to the Civilization series, prior to Civilization V, multiple units could be stacked on a single tile. The two features are very different, but the original statement was nonetheless incorrect, and we apologize for the error.