Flag of Germany
When Heinrich XI, Prince Reuss of Greiz was appointed by Joseph II, Holy Roman Emperor to rule the then-new Principality of Reuss-Greiz on 12 May 1778, the flag adopted by the "Fürstentum Reuß-Greiz" was the first-ever appearance of the black-red-gold tricolour in its modern arrangement in any sovereign state within what today comprises Germany – the Reuss elder line that ruled the principality used a flag whose proportions were close to a "nearly square"-shape 4:5 hoist/fly ratio, instead of the modern German flag's 3:5 figure.
Tricolour (flag)
The flag of Germany (black-red-gold) originated as the flag of the revolutionary, anti-monarchist Freikorps of the 1830s and was later adopted by the republicanist bourgeoisie, at the time known as "Dreifarb", a German calque of "Tricolore". This flag was a symbol of opposition against the German "Kleinstaaterei" and the desire for German Unification. It was at first illegal in the German Confederation, but was adopted as the national flag at the Frankfurt Parliament of 1848/9. The flag of Belgium was introduced in a similar context, in 1831, its colours taken from the flag used in the Brabant Revolution of 1789.
The first national flag of the New World inspired by this symbolism was the flag of Mexico, adopted when the First Mexican Empire gained independence from Spain in 1821.