Star Trek aliens traditionally were intended to represent individual human traits, i.e., Vulcans=Logic, Ferengi=Greed, etc. I could never figure out what they were supposed to represent with all the different Xindi factions.
I always was under the impression they serve as overdrawn parallels for ethnic groups and how they were seen from a US-centric view starting with TOS. Klingons as russians, Romulans as the japanese, Cardassians as nazi germany and Ferengi as the logical conclusion of capitalist, hedonist 20th century americans.
I would switch the Klingons and Romulans. The Klingons are the Imperial Japanese and Romulans are the USSR. The klingons have ritual suicide and the 'samurai' warrior ethic. And Romulus has secret organizations that disappear people, which is blatantly Communism.
Originally in TOS, Klingons faced off against the Federation in a Cold War allegory. This was enforced by the Organians, as of the first Klingon episode, Errand of Mercy
, so the Klingons were initially analogous to the Soviets.
The Romulans debuted in Balance of Terror
, an episode based on a WWII submarine movie
depicting a US Navy destroyer versus a German U-boat. Thinking of the Romulans as patterned after Germans would therefore be more apt than thinking of them as patterned after the Japanese. However, Romulans later assumed an allegorical role patterned after the North Koreans
, in The Enterprise Incident.
None of these allegorical roles are absolute, and both Klingons and Romulans have been revised a great deal since the TOS days.
When it comes to ritual suicide, I've seen a Romulan commander blow his own ship up to avoid capture (in BoT), but I don't recall a Klingon ever doing anything similar.