There are nineteen nations in the World Top Incomes database that have data going back to the 1970s. This figure shows the average share of the top one percent (adjusted for differences in the nations included in particular years). It declined from 1970 to the early 1980s, and then increased. The big jump in 2012 is probably not meaningful, since it's based on only one or two nations.
I then calculated a linear trend for each country adjusted for these differences. Adjusting is important, because otherwise estimates of trends would be distorted by the particular years for which data were available: e. g., an "average" country for which the data began in 1985 would seem to have faster growth than one for which the data began in 1970. The rankings, taking the United States as the standard of comparison:
-0.21934 New Zealand
The United States is #1, but it's not a simple case of the United States versus everyone else--there are substantial differences among the other countries.