The newer the union, the more fragile; the older, the more durable. Yugoslavia, for example, only existed for a couple decades before it dissolved. The USSR (most of which was previously the Russian Empire), only existed for a a short time (decades to a few centuries, depending on area) before dissolving. Contrast this with any of the constituent parts of those collapsed states. E.G. Russia proper is quite stable; it's not going to be dissolving into Muscovy, Novgorod, etc.
The centralizing process in geopolitics isn't linear (more like two steps forward, one step back), but it's clearly present. A look through an historical atlas makes this plain. What does this mean? It means both that world government is likely and, eventually, would be stable (i.e. not break up in civil war, etc), and that final, stable state would then be advantageous (no inter-state war, and no civil war).
Despite you looking at me like I'm a talking dog for saying I favor world government, it's perfectly natural for people who (a) hate war, and (b) have no time for nationalism, to look forward to such a development. Mises was of the same view, as have been many other liberals over the last several centuries. This is a part of the liberal tradition which has been forgotten (or intentionally buried by persons who benefit from war and nationalism), not a new one.