The game contains rules determining when the Soviet Union, United States, and Italy may choose to enter the conflict.

The game is played with the Commonwealth (consisting of the United Kingdom, Canada, India, Australia, South Africa and numerous territories and colonies), France, China, USSR and the United States of America forming the Allies and Germany, Italy and Japan forming the Axis.

Aggressive Allied play - such as declaration of war on neutral minor countries - will slow US entry.

Days of Decision starts gameplay in 1936 and allows for a far greater range of actions in the political spectrum.

The weather influences combat modifiers, naval ability to spot enemy fleets, supply range, aircraft mission eligibility, land unit movement allowance and how fast the end of turn impulse marker advances after each impulse.

The exact number of movements allowed depends on the Major Power and reflects its overall size and organisation.

At the beginning of each round of air-to-air combat, each side can opt to abort its remaining aircraft and return them to an eligible hex.

To initiate combat, two fleets in the same sea area either commit or submerge their submarines, then perform die rolls to determine whether the units (which can also include land-based and carrier-based aircraft) spot each other, which side has the element of surprise and to what degree.

If at least one stack of units is deemed to spot the enemy fleet and neither side uses surprise to evade the other, combat is initiated.

The right to select the combat type is conferred firstly by surprise, secondly by aircraft, and thirdly by submarines facing enemy convoys.

Naval air combat requires that an air-to-air battle is fought if either player has fighters allocated to defending their units.

ASW is provided by surface warships (each of which is assumed to always have a screen of destroyers), by naval bombing factors or, in the late war, by Western Allied convoys.

The sum of the relevant type of combat factors is cross referenced with the number of units in the opposing fleet to determine results.

In naval air combat, the first and subsequent odd-numbered targets are selected by the owner of the attacking bombers.

Each result must be assigned to a unit, which then makes a roll to determine if its armour reduces the damage by one level.

After all results are assigned, each side has the option of aborting all remaining ships in the combat, returning them to an eligible port and flipping them.

In the November 1989 edition of Games International (Issue 10), Mike Siggins greatly admired the production values, saying, "The box [...] contains 1000 counters, maps and play aids and these are all among the best you will see in the hobby."

Although he found the rules long and complex, he admitted that they "make an acceptable job of conveying the system to the reader, and their length is partly due to the copious examples, which is no bad thing".

He pointed out that this is a monster game that would take large amounts of time, saying, "my estimate is that at least twenty hours once you know the system".

[1] Harry Rowland explained what a great achievement receiving the world record was, “World in Flames: the Collector’s edition was released in 2018 as a hard-mounted board game unlike previous versions which, like most games in this genre, use paper maps.

It also includes, in the Deluxe version, 4900 counters and 192 pages of rules, 22 campaigns, and players’ & designer’s notes, that makes World in Flames a hobby in a box.” “World in Flames: the Collector’s Edition is the culmination of millions of hours testing the game to its limits by tens of thousands of gamers over the years; we couldn’t have done it without their help.

“The international nature of modern gaming is clearly displayed in this project with artists contributing from Mexico, the USA, Germany, Czechia and Australia; rules, testing and editing from around the world, and design in Mapleton."

EFKO have given World in Flames: the Collector’s Edition the lavish attention this game deserves to make this award possible.” EFKO owner, Mirek Kotik, said that his company was proud to have taken part in the project to make history with this world record, “It is a deserved recognition of our team’s professional approach to printing the most complex projects in a time critical manner, paying attention to the smallest detail in every game we produce.” At the 1986 Origins Awards, World in Flames won the 1985 Charles S. Roberts Award for Best 20th Century Game.