The Dannebrog flag of Denmark of 1219 (a crusader flag), with its distinctive cross shifted to the hoist, was copied by the other Scandinavian countries: Finland (1917), Iceland (1944), Norway (1905), and Sweden (1442).
The Netherlands flag - the Prinsenvlag (1572) using the the blue, orange (red) and white livery colours of the Prince of Orange - was copied by the Russian flag (1696) which gave rise to the blue, red and white colours chosen by the Pan-Slav Congress of 1848 at Prague and thus adopted as the basis for the national flags of Croatia (1991), Czechia (1918), Serbia (2006), Slovakia (1992), and Slovenia (1991).
The American Stars and Stripes of 1777 (one stripe for each state) was similarly copied by Cuba (1902), Greece (1828), Liberia (1847), Malaysia (1963), Togo (1960), and Uruguay (1830).
The French vertical Tricolor adopted in 1790 (white for France; blue and red for Paris) was copied by Andorra (1866), Belgium (1831), Cameroon (1960), Chad (1960), Guinea (1958), Guinea-Bissau (1974), Italy (1805), Ireland (1922), Mali (1960), Mexico (1821), Moldova (1990), Romania (1868), and Senegal (1960).
The Union Jack of 1801 was incorporated into the flags of four of its former colonies - Australia (1901), Fiji (1970), New Zealand (1902) and Tuvalu (1997). This is the Red Cross of St George for England on the Red Cross of St Patrick for Ireland superimposed upon the White Cross of St Andrew on a blue field for Scotland.
The blue, red and yellow of the Republic of Gran Colombia of 1819-31 (golden America separated by blue sea from bloody Spain) were adopted by its three successor states of Colombia, Ecuador and Venezuela.
Ethiopia was the only African country to (with difficulty) maintain its sovereignty during the 19th Century European “scramble for Africa”. Its green, yellow, red flag adopted in 1897 (the colours of the Rainbow in the book of Genesis) thus became the Pan-African colours, a model for other African and Afro-Caribbean countries when they achieved independence in the 20th Century. As a result, the following countries adopted those colours for their flags:
Benin (1960), Burkino Fasso (1960), Cameroon (1969), Central African Republic (1960), Comoros (2002), Congo Brazzaville (1960), Dominica (1978), Eritrea (1993), Ghana (1957), Grenada (1974), Guinea (1958), Guinea-Bissau (1973), Guyana (1966), Mali (1960), Mauritius (1968) , Mozambique (1983), Namibia (1990), Sao Tome & Principe (1975), Senegal (1960), Seychelles (1996), St Kitts & Nevis (1983), South Africa (1994), South Sudan (2005), Surinam (1975), Togo (1960), Uganda (1962), Zambia (1964), Zimbabwe (1980).
Similarly, the Ottoman Empire was one of the few Islamic states to preserve its independence (despite Russian attacks) during the age of European expansion. Subsequent Moslem states thus copied its crescent flag ( adopted in 1793 to symbolise the lunar calendar in Islam), namely Azerbaijan (1991), Comoros (2002), Iran (1979), Libya (1951), Malaysia (1963), Maldives (1965), Mauretania (1960), Pakistan (1947), Tunisia (1956), Turkey (1923), Turkmenistan (1991) and Uzbekistan (1991).
In contrast, the black, green, red and white colours of the flag of the Arab nationalist revolt against the Ottoman Empire in 1916 were adopted by most Arab countries which gained independence thereafter, ie Iraq (2008), Jordan (1946), Kuwait (1961), Libya (1956), Sudan (1956), Syria (1946) and United Arab Emirates (1971).
The Argentine flag (blue and white of the Order of Charles III) was adopted by the Federal Republic of Central America 1823-40 and the successor states of that republic, ie Costa Rica, El Salvador, Guatemala, Honduras, and Nicaragua.
The United Nations Organisation sponsored the creation of four countries, which accordingly copied the blue and white of its standard of 1946 (blue for the sea; white for peace), for Micronesia (1990) and Somalia (1960).
Communist China (1949) and Vietnam (1954) have national flags modelled on that of the former Soviet Union ie red for revolution, on which there is a five-pointed star representing the Communist Party.