Declaration of War triggers

the game starts with Germany and Italy at war with GB,France, and ANZAC. While in the pacific Japan is at war with china. Every country besides U.S. may declare war whenever they like and every country including U.S. will be at war once attacked by a country. They are only at war with that country however not the entire Axis or entire Allies.
unique rules:
USA= Axis attack on North America, London is captured (optional)
Japan= any allied units present in china
GB= attack of DEI
ANZAC=attack of DEI

may have forgotten some, this was just off the top of my head :p

For that you just need a note like what triggered US entry into ww1.

Yes.
Although technically, I believe it simply allows the US to declare war on Japan at the beginning of the US turn. I don’t think they have to if for some reason they don’t want to.
Attacking the UK will automatically bring the Anzac into the war though.

@BluGerman:

Every country besides U.S. may declare war whenever they like

Russia may only declare war on the European Axis (Germany or Italy or both) starting at round 4. If Russia has been declared war or attacked by one of those powers earlier, Russia may declare war to the other one.

UNITED STATES:
1> Any attack on US units or territories by an Axis power will bring the US into the war against that power. The US may then declare war on any or all Axis powers.
2> If any Axis power takes control of any territory in North America, the US may declare war against any or all Axis powers.
3> If any Axis power takes control of London, the US may declare war against any or all Axis powers.
4> If Japan makes an unprovoked declaration of war against UK/India or ANZAC, the US may declare war on any or all Axis powers.
5> If the United States is not at war by the Collect Income phase of it’s third turn, the US may declare war on any or all Axis powers.
SOVIET UNION:
1> The Soviet Union may not declare war on Germany or Italy until the combat move phase of it’s 4th turn.
2> The Soviet Union may declare war on Japan during the combat move phase of any turn.
3> If Germany or Italy attacks the Soviet Union before turn 4, the Soviet Union may declare war on either one or both countries.
4> If any Axis power takes control of London, the USSR may declare war on Germany and/or Italy.
JAPAN:
1> Any movements of ANY Allied units into or through China will be considered a declaration of war against Japan.
1a> In the case of UK/India and ANZAC, Japan may go to war with these powers without provoking the United States.
UNITED KINGDOM/INDIA:
1> Attacks by Japan on Dutch possessions is considered an attack directly on UK/India.
ANZAC:
1> Attacks by Japan on Dutch possessions is considered an attack directly on ANZAC.
NOTE: ANZAC and UK/India, although separate powers, act together. An attack on one is considered an attack on both.

@knp7765:

Any movements of ANY Allied units into or through China will be considered a declaration of war against Japan.

An Allied power must declare war on Japan (at the beginning of that power’s Combat Move phase) before moving units into or through China.

@knp7765:

Attacks by Japan on Dutch possessions is considered an attack directly on UK/India.
Attacks by Japan on Dutch possessions is considered an attack directly on ANZAC.

Japan must declare war on UK-ANZAC (at the beginning of Japan’s Combat Move phase) before attacking a Dutch territory.

@knp7765:

UNITED STATES:
1> Any attack on US units or territories by an Axis power will bring the US into the war against that power. The US may then declare war on any or all Axis powers.
2> If any Axis power takes control of any territory in North America, the US may declare war against any or all Axis powers.
3> If any Axis power takes control of London, the US may declare war against any or all Axis powers.
4> If Japan makes an unprovoked declaration of war against UK/India or ANZAC, the US may declare war on any or all Axis powers.
5> If the United States is not at war by the Collect Income phase of it’s third turn, the US may declare war on any or all Axis powers.
SOVIET UNION:
1> The Soviet Union may not declare war on Germany or Italy until the combat move phase of it’s 4th turn.
2> The Soviet Union may declare war on Japan during the combat move phase of any turn.
3> If Germany or Italy attacks the Soviet Union before turn 4, the Soviet Union may declare war on either one or both countries.
JAPAN:
1> Any movements of ANY Allied units into or through China will be considered a declaration of war against Japan.
1a> In the case of UK/India and ANZAC, Japan may go to war with these powers without provoking the United States.
UNITED KINGDOM/INDIA:
1> Attacks by Japan on Dutch possessions is considered an attack directly on UK/India.
ANZAC:
1> Attacks by Japan on Dutch possessions is considered an attack directly on ANZAC.
NOTE: ANZAC and UK/India, although separate powers, act together. An attack on one is considered an attack on both.

Russia can declare war on european axis if london falls.

Dang it! Forgot that one. Just edited my previous post. Thanks ghr2.