Swiss Confederation (modern federal state)
Who & why: a brief 1847 civil war, the Sonderbund War, between a Catholic conservative cantonal alliance and the liberal Protestant majority ends in weeks with the conservatives' defeat, clearing the way for a new 1848 federal constitution that turns the old confederal alliance into a single federal state with a national government, while still leaving cantons wide autonomy and direct-democratic rights unusual anywhere else in Europe. The constitution is revised in 1874 and comprehensively rewritten in 1999, but the federal structure itself is unbroken from 1848 onward. Switzerland stays neutral through both World Wars, joins the UN only in 2002, and remains outside the EU by referendum choice while trading closely with it.
What it represents: the same white cross on red carried informally since the medieval confederacy, now the fixed national flag; a federal decree in 1889 standardizes the cross's arm proportions (each arm one-sixth longer than it is wide) for the first time, the exact spec still in force today.