After Revolutionaries declared their plan, there was a speculation of why do the Revolutionaries plan to declare the war right in Reverie.
What’s the point, if you could just announce it at a safe distance, not in the Holy Land Mary Geoise, which will be protected by Marines. It is very risky indeed. Firstly, let’s look at the facts that we have:
1.The Revolutionary Army’s business is with the Celestial Dragons, not the countries. That was mentioned by Koala.
2.The Reverie is a massive event with participants from over 50 countries. It was announced during Zou arc.
3.There is a high level of discrimination against Longleg/Fishmen/Giants, etc. and the main reason are the Celestial Dragons, who established this world as it is. Keep in mind, in Chapter 906 a Celestial Dragon was looking at Shirahoshi with some dirty plans.
4.Revolutionaries are trying to recruit more allies as it was seen when Belo Betty gave a card to the citizens of Rurussia Kingdom.
I guess, from this point it becomes more clear. The Reverie was always a key event where main decisions were made, conflicts started. The Revolutionaries will declare the war to Celestial Dragons right in front of all Kings. Remember, that during Reverie there probably will be attempt to kidnap Shirahoshi and the tension between the World Government and the countries that were discriminated or suffered from their previous leaders (Ryugu, Sakura) will rise.
The main reason for Revolutionaries to announce the war against the Celestial Dragons might be that they will also call the leaders to join it. This in return, will divide the world into two: those who support the World Government and the allies of the Revolutionary Army. That also goes well with Dragon, as he is D. – “Natural enemy of a God” – and also this declaration will create a chaos in the world. This also goes well with D. reputation. Kingdoms that aren’t part of the Reverie also will participate and choose their side.
Now, it makes clear why Revolutionaries would want to ambush the Marie Geois for the declaration of war.
*Theory by ki_dragon817