The last 40-50 years have been pretty stable. But even so I’d guess that 20% of world governments have functionally gone out of business.
If you pick the 20th century, then the number of governments that have “failed” is really large as a proportion of total governments. We think of countries like France as having been around for hundreds of years, but their current constitution is only 62 years old. Romania had three different governments in about 50 years. Japan, China, and Vietnam all replaced their governments. Czechoslovakia came into being and disappeared.
If you pick the 20th century, then the number of governments that have “failed” is really large as a proportion of total governments. We think of countries like France as having been around for hundreds of years, but their current constitution is only 62 years old. Romania had three different governments in about 50 years. Japan, China, and Vietnam all replaced their governments. Czechoslovakia came into being and disappeared.