Today is Syttende Mai (17 May), which is the founding day of modern, constitutional Norway (officially Constitution Day). It feels like a super-arbitrary day most everywhere in the world except, perhaps, Scandinavia and Northern Minnesota where my people hail from.
Every country has their day - as I started this post, it occurred to me that Haiti's Independence Day is January 1st (1 January 1804), the official end of the Haitian Revolution. Starting on January 1st, I figured I would start another perpetual post* which would function as a calendar outlining founding dates of the countries of the world. I'll start with the one's I know and think of off-hand (which is these two, plus the 4th of July^), and build from here (I'll appreciate anyone's input in the comments section!, or I'll add as I notice them going about my daily life):
January
1 - Haitian Independence Day
May
17 - Syttende Mai (Norway's Constitution Day)
July
1 - Somalia's Independence Day
1 - Canada Day (formerly Dominion Day until 1982 - which sounds much more bad-ass, Canada and you may want to consider switching back)**
4 - United States of America's Independence Day
September
16 - Mexican Independence Day (Celebration of the Mexican War of Independence with this date marking the start of the Hidalgo Revolt in 1810)
December
1 - Romania's Great Union Day (marking the 1918 unification of Transylvania, Bessarabia, Bukovina & The Romanian Kingdom)
* a perpetual post is one on Roman Numeral J that gets updated over the course of months & years, and may never truly be finished, but is a work in progress toward some declared end goal (e.g. the Lost Last Fives, the Vodka Ranking, and the Star Trek Chronology).
^July 4th feels significant - until you spend an American Independence Day outside of the United States. America does a pretty good job of lampooning itself most of the time, but that's nothing until you experience a bunch of people from all over the world throwing you and your American friends a party that is heavily sarcastic (and always features a sparkler, which i think is the only firework that is partly legal in most sensible countries)
** it's a small sample size thus far, but on discovering that both Canada Day & Somalia's Independence Day both occur on the same day, I wonder if we will come to discover that a disproportionate amount of founding days will be on the first of the month. Like the start of a month feels like a good 'reset button' when you're starting up a new country (as opposed to most countries "happening" on some random date).