You can actually watch Hetalia in any order. But here's a guide if you want to watch it by release order. Those with asterisks (*) are the parent stories.
Basically, Axis Powers > World Series > The Beautiful World > The World Twinkle > World★Stars.
Hetalia Watch Order:
* 1. Hetalia Axis Powers (Jan 24, 2009 to Mar 5, 2010) | ONA | 52 episodes × 5 min. per ep. - Prequel / Parent Story
* 2. Hetalia World Series (Mar 26, 2010 to Mar 11, 2011) | ONA | 48 episodes × 5 min. per ep. - Sequel / Prequel / Parent Story
3. Hetalia Axis Powers Fan Disc (May 25, 2010) | OVA | 1 episode × 10 min. - Side Story
4. Hetalia Axis Powers Movie: Paint it, White (Jun 5, 2010) | Movie | 1 episode × 1 hr. 20 min. - Side Story
5. Hetalia World Series Specials (Mar 25, 2011 to Sep 24, 2012) | Special | 4 episodes × 5 min. per ep. - Side Story
* 6. Hetalia: The Beautiful World (Jan 25, 2013 to Jun 21, 2013) | ONA | 20 episodes × 5 min. per ep. - Sequel / Parent Story / Prequel
7. Hetalia: The Beautiful World Specials (Apr 24, 2013 to Oct 30, 2013) | Special | 4 episodes × 5 min. per ep. - Side Story
8. Hetalia: The Beautiful World Extra Disc (Feb 26, 2014) | OVA | 1 episode × 5 min. - Side Story
* 9. Hetalia: The World Twinkle (Jul 3, 2015 to Oct 9, 2015) | ONA | 15 episodes × 5 min. per ep. - Sequel / Other / Parent Story
10. Hetalia: The World Twinkle Specials (Oct 28, 2015 to Dec 25, 2015) | Special | 3 episodes × 5 min. per ep. - Other
11. Hetalia: The World Twinkle Extra Disc (Feb 24, 2016) | OVA | 1 episodes × 12 min. - Side Story
* 12. Hetalia World★Stars (Apr 1, 2021 to Jun 17, 2021) | ONA | 12 episodes × 5 min. per ep. - Side Story / Sequel / Prequel
13. Hetalia World★Stars Specials (Jul 28, 2021) | Special | 3 episodes × 5 min. per ep. - Sequel
If you wan't to watch in chronological order, start with (1) Hetalia Axis Powers followed by (3) Hetalia Axis Powers Fan Disc and (4) Hetalia Axis Powers Movie: Paint it, White before (2) Hetalia World Series and then (5) to (13) as listed.
I watched these out of order with subtitles. I will rewatch these in release order with dub.
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Reading Order:
1. Hetalia Axis Powers (Mar 28, 2008 to Jun 29, 2013) - Parent Story
2. Hetalia World☆Stars (Sep 22, 2014 to ?) - Side Story
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Genre: Comedy
Themes: Anthropomorphic, Gag Humor, Historical, Parody
Tags: Country, Nation, World War, Franchise
Club: Axis Powers Hetalia Club https://myanimelist.net/clubs.php?cid=6455 (Inactive)
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Official Sites:
http://hetalia.com/twt/
http://musical-hetalia.com
Twitter (X): https://twitter.com/animehetalia (@animehetalia)
Wikis:
https://en.wikipedia.org/wiki/Hetalia:_Axis_Powers
https://hetalia.fandom.com/wiki/Hetalia_Archives
https://hetalia.kitawiki.net
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There's Hetalia Archives but I need a Hetalia episode to chapter (+ musicals, drama CDs, etc.) converter badly. Ugh, I don't think I could do it; there are so much media material.
Anime: https://hetalia.kitawiki.net/index.php?title=Category:Anime | https://hetalia.kitawiki.net/index.php?title=List_of_Hetalia_episodes
Manga: https://hetalia.kitawiki.net/index.php?title=Category:Manga
Audio: https://hetalia.kitawiki.net/index.php?title=Category:Audio_Media | https://hetalia.kitawiki.net/index.php?title=List_of_Hetalia:_Axis_Powers_CDs
Musicals: https://hetalia.kitawiki.net/index.php?title=Category:Musicals | https://hetalia.kitawiki.net/index.php?title=HetaMyu