It has been my dream to see Aikido being united all over the world
What do you mean by "united"?
What we call aikido today has its roots in the same ryu or better teh same kaiso.
But different lines of tradition have given what is called aikido different shapes depending on the teachers (shihan) they follow.
Saito sensei, Yamaguchi sensei, Shioda sensei, Nishio sensei, Mochizuki sensei, Tohei sensei ... and a lot of other names.
So what does "united" mean:
Doing ikkyo the same way?
Being organised in just one Organization?
(How should it be structured: Like a western federation or like a japaneze ryu?)
If you mean
Creating situations where any Aikidoka can cross-train at any Aikido dojo anywhere in the world without feeling guilty of "betraying" one club over another, or without feeling the pressure of choosing only one club over another.
then be aware that this form of unity exists. In my surrounding this is truly possible. And is done by a lot of practioners.