
Despite all of this, however, the Earth Federation is the eventual victor in each of these conflicts, if only through outlasting the various threats to its survival. By the time of Victory Gundam (60 years after CCA), the Federation is so weak and ineffectual that it falls to a militia to oppose The Empire. Afterwards, in Mobile Suit Gundam: Char's Counterattack, even though Zeon has been defeated twice already, the Earth Federation is so weak that the Neo-Zeon nearly make the Earth uninhabitable and only a miracle caused by Amuro's death stops it. Seven years later, in Mobile Suit Zeta Gundam the Earth Federation has weakened to the point that the remnants of Zeon are still a serious threat, and a State Sec organization is intentionally sabotaging the Federation from within so that they can take over. The Federation won the One Year War in Mobile Suit Gundam through superior power and production capability, but at the cost of half of the world's population.
The Earth Federation from the Universal Century universe of Gundam is this, in a pattern that echoes Gibbon's Decline and Fall. Before its decline it had also conquered pieces of the (offscreen) Tasan Empire, a second example of this trope. The Beelzenian Empire in the Evillious Chronicles franchise is an example of this as the centuries go on, losing larger and larger chunks of territory until it's only a shell of its old self. After the end of the Universe Survival saga, Frieza decides to rebuild his empire. When the resurrected Frieza tries to get revenge on Goku, the last remnants of the army are wiped out. After Freeza's and Cold's deaths, the empire lost most of its territories and Sorbet is barely holding the last pieces together when he decides to revive Frieza out of desperation. At its peak, it controlled about 70% of the universe. The Planet Trade Organization, Frieza's empire, has become one by the time of Dragon Ball Z: Resurrection ∟ and Dragon Ball Super.
However, in order to get the rest of the world on their side and retain their position of power, they've declared war on Paradis Island in the hopes of wiping out the Eldians once and for all so that they're free from the threat of being overthrown, as there's been a constant power struggle between Eldia and Marley for almost two thousand years.
Marley itself is slowly becoming this, as new weapon technology means that the Titan Shifters they've relied on for so long are no longer as powerful against their enemies as they once were. They settled on the island of Paradis as the Kingdom of Marley overthrew and exiled them. Attack on Titan has revealed that the Walls are in reality the last bastion of the once proud Eldian Empire, formed by Eldians led by the royal Fritz family.