Adoption Was Slow, Uneven and Political
16th-20th centuries
The calendar did not sweep the world in 1582. Catholic states adopted at once; Protestant and Orthodox states took between a century and three and a half centuries, for confessional and political reasons as much as scientific ones.
The staggered dates
Spain, Portugal, Poland and the Italian states changed in October 1582. Much of Protestant Germany and the Dutch Republic waited until 1700. Great Britain and its colonies changed in September 1752, dropping eleven days by then. Russia changed only after the 1917 revolution, in 1918; Greece changed its civil calendar in 1923.
Why Protestants hesitated
Early Protestant resistance was largely about the source of the decree rather than the mathematics — a reluctance to receive a calendar promulgated by papal authority. The astronomy was generally conceded long before the calendar was adopted, which is a useful precedent for reading the Eastern response fairly.
Civil is not ecclesiastical
This distinction is repeatedly missed. A state adopting the Gregorian calendar for civil affairs says nothing about what its church does liturgically. Greece adopted civilly in 1923; the Church of Greece's decision about fixed feasts is a separate act, and the Paschalion is separate again.