Some other worlds have trees, animals, oceans, and/or, etc.
Some have more than one moon.
Some have no moon.
Different kinds of buildings, terrain, gasses, germs, pollens, air, etc.
No two worlds are alike, and no two races alien to one another can share a world to sustain life.
Our bodies fit only our own worlds that our race has developed on since its beginning.
However, when we say "all other worlds" that term is a tiny bit loose, because the amount of worlds and life is endless and nobody knows all about all life.
It is impossible to speak for absolutely every body or every place because of the diversity. [1]
Living on other worlds
When the time comes, we may need/want to colonize other planets.
But all planets which can be inhabited probably already are, and resources we might want, would already be claimed by other civilizations.
Since the alliance of races is that big, this has probably occurred before.
Planet Suitability
If the time comes when we can't live here, we are going to die.
If we can't fix our own world to live on, we can't fix another.
Our planet is perfect for us because we are "made from" it.
Another planet would need even more fixing and in ways that we are not capable of doing.
Every planet is different.
And every planet that has a race of people is just as different.
Any race only wants its own planet to live naturally on - that is the best way.
The second best (easiest) way is to live in space crafts.
There are many more planets, than planets with people living on them.
Bio-compatibility
A race can't move to another world.
They can visit only.
If a race tries to move to another world, to move into another world, to live there, the race immediately changes the circumstances of the new world.
Two things happen, the world is changing and the people are changing.
it's like trying to hit a moving target.
You can't.
How many people have to die instantly before the whole race of them start to change to fit the new world?
And the presence of the race is also changing the world at the same time.
Planet Class M
Any world might sustain life because the life inhabiting the world has physically evolved with the unique circumstances of the world from the beginning of its development there.
Just because the temperatures of two different worlds are found to be alike, that does not mean the life can share the worlds.
It only takes one difference to make a world uninhabitable for alien life.
There are so many variables in so many characteristics of every world that the uniqueness is like that of snowflakes.
Life fits exactly only its original world.[2]
Resources
Advanced civilizations use resources, but they don't use them up.
There is plenty, and all need and use such diverse resources that they don't have any need to fight over them.
Instead, they help each other.
Don't let this sound too perfect, though.
There are problems, just not many, and they solve them.
Mars
Considering all the life and history, there must have been desperate times when races have had to move to another planet.
I only imagine this because of some things that my alien friends have said about Mars, when the race that lives there was faced with sudden destruction of their atmosphere and they had to make decisions of how to survive.
They considered searching for another planet they could move to, but instead they modified the one they have and moved everybody underground.
It was much easier to control the atmosphere of their own planet than that of any other.
Advanced Worlds
I know a little bit about a few other worlds specifically, and all other worlds generally from my own experiences and teachings by alien life.
All races and worlds are different with some same and some unique circumstances.
But almost all other races are much further advanced and evolved than we are.
Advancement does not bring peace, though.
Peace brings advancement.
So no matter how large or small advanced races of people are, they have peace.
All basic needs are met for every person on a world through the organization of their leadership.
That is the major difference I see between us and all advanced races.
