A true, lasting peace is impossible. The only real reason we have any form of "peace" nowadays is through the threat of nuclear weapons, which if actually used in any significant capacity would result in a global nuclear war, likely wiping most if not all of humanity out. Keeping "peace" by means of fear of massive retaliation, basically saying "If I'm going down the I'm taking you with me" from every major wold power. There are simply too many differences in ideology between different nations and peoples. As long as there are at least 2 people left in the world, chances are that one of them will eventually want the other one dead.
There are too many regional animosities going back centuries, too many instances of one groups self interest being at odds with another groups, human nature still too ready to resolve concerns with violence for world peace to be achieved.
Locally peace can be achieved and can last, it is to be hoped for and hopefully strived for.
We are never really at peace. We just tell ourselves, or rather our brain likes to create a sense a security. This sense of security makes us think we're at peace. No matter where you are, some kind of danger, no matter how small could occur, no matter at what time.
I do not think there will ever be a peace on a global scale. I think that the idea of peace is something we all should always fight for even though we all know that it can never happen. That does not mean that we should abandon all measure to fight for it.
Illusion is merely how we ourselves define a different idea. The idea is just the idea. What is true is true, no statement can work around that. So if the idea is true to itself, not to another perception of it, then then how we perceive it is merely an attempt to conjecture what is.
I personally think that peace can be a reality because whatever an individual can motivate themselves to do anything and everything is possible. I personally think that peace can be a reality as long as that individual has a mindset to having peace. I personally think that peace can be a reality but it does take time which is patience.