Details of Zero Requiem

Zero Requiem does omit number of details that might make people misunderstand what happened and why it happened. They only cover politics at glance as then just bring you the outcomes. After all he did not mean it figurately when he said that 'From this moment forward the world belongs to me.'.

So, after Lelouch defeated Schneizel, took control of Fleija and made that announcement, what did he do?

First just as he intended with that discussion with representatives of the UFN he joined the UFN but did not reduce voting power of his country. That gave him controlling vote and essentially allowed him to rule both Brittania and UFN simultaneous. As per announcement during the parade he was Chairman of the UFN. That alone allowed him to turn two biggest nations into one.

Lelouch as Zero of course created UFN himself, but UFN members did not knew that. So UFN members saw that as usurpation of their organization by their former enemy.

Then he used threat of using his forces and Fleija on all the remaining nations in the world and forced them to join UFN. Thus, turning UFN into an effectively world government and himself into a ruler of the entire world. Other nations did not like that, but there was nothing they could oppose the guy who has Fleija and does not hesitate to use it.

He also used controlling vote in UFN to reappoint himself as CEO of Black Knights. For most Black Knights, who did not know Lelouch was Zero, that was not a reappointment but rather usurpation of their organization by a former enemy. However, there was nothing they could do about it.

So Lelouch united the entire world.

However, all these actions made Lelouch very unpopular. Most saw it as unapologetic tyranny as gunpoint. So, world hated him. Many went underground to resist his new rule secretly. Lelouch did not liked that there is resistance, but what he could do to stop even them.

Lelouch ruled the world, but everyone hated it. They hoped that some kind of resistance hero, such as Zero, will overthrow Lelouch's rule and make world free again. 

Being cunning enough Lelouch figured out just what to do to give them just that: Zero Requiem. Zero will just reappear and in a staged scene will 'kill' Lelouch. World will be free from tyranny and live free again.

No one knew Lelouch was Zero, in fact it was implausible to think that Lelouch was Zero in the first place. Sure, anyone could be under the mask, but he is likely Japanese or any other ethnicity, oppressed by HBE. Black Knights executives have never announced that Lelouch was Zero, because they thought that even their own members will think they are insane to say something like that, that is how implausible that was.

After Zero Requiem not even underground resistance had any reasons to oppose his rule. Cornellia, Gilford and Viletta joined new world order. His former Black Knights notable members became prominent members of new world order. Zero and them became heroes of the world, just as Lelouch originally intended.

So Lelouch achieved all that he wanted. 

Because of Code of Immortality, he did not die in the process.