Hey, for Germany check out this previous post of mine!

• How and why did people accept nationalism when it first emerged?

• How did Prussia come to dominate all the other German states?

I like the TL;DR from my first post though:

• French Revolution introduced the philosophical concepts of a nation of equal citizens + the rise of the secular state loyal only to its people.

• ...along with the literal, legal application of removing the privileges of aristocracy and the church. The former was not so much applied to all of Germany but it was, still, heavily performed.

• The plummeting of religious belief in Europe created a void of "social glue" which held society together.

• West Germany would be heavily mediatized giving the power to a few, powerful Princes with a large base constituency rather than a decentralized band of Church, Knightly, and Imperial land with varying loyalty: Local Germans had German land now, more aptly.

• Massive boons in the field of communications, industrialization, transportation, and literacy created an interconnected world like never before.

• The memory of French dominance for decades, the removal of the Holy Roman Empire and the persistent threat of internal and external conquest, created the universal want/need for a strong centralized German state for protection.

• With the shared communication, literacy, etc. clubs and societies sprung up like wildfire all speaking and sharing to "German" history, a shared German culture, exemplifying "German" characteristics and traditional clothings and foods. Everyone could now communicate with everyone, a proverbial melting pot, and now they were all sharing the wealth of history and culture from their corner of Germany.

Everyone else began their own journeys at their own times though. France began in 1792 like I said above. Germany began, arguably, in 1803 (mediatization) and 1805 (end of the HRE) but certainly in 1815 after Napoleon. The Slavic people would begin theirs as they found common identity of oppression under their Austro-Hungarian masters. The Poles under their common oppression from basically everyone who wanted to divvy up their land and people; a shared status of minority split between 3, 4, even 5 other states at times. It took the Russian people, arguably, until 1917 to truly begin their revolution. It's a very case by case basis for why a people took hold of nationalist thought so we must understand it wasn't a "lightswitch"; it was a genie out of the bottle which slowly gripped everyone it touched through various ways and just happened to occur at the most opportune social period in human history. It took some longer than others though and we can't forget that.