So I've been giving this some more thought recently...
The Klingons are actively hostile towards mankind beginning in 2223 (or thereabouts), culminating in the intervention of the Organians in 2266. They remained pretty nasty until 2293, when Praxis exploded and the UFP offered a helping hand. In 2343, the <i>Enterprise-C</i> sacrificed itself defending the Klingon colony of Narendra III from Romulan attack, leading to even friendlier relations between the Empire and the UFP.
So what were relations between the powers like in the 22nd century? I imagine that the Klingons were a lot like Tsarist Russia at the time, controlling a fairly large empire and working on expanding their influence in the region. I am going to operate under the assumption that the Klingon Empire underwent a revolution of sorts during the 2220s, leading to a change in the oligarchic nature of their government and the institution of a quasi-fascist junta with monarchic overtones (like WW2 Japan), perhaps the result of the more militant of the High Council members taking the forefront. This revolution was followed by a period of imperialistic conquest, and <b>that</b> led to conflict with the United Federation of Planets (i.e. annexing worlds in UFP space, attacking Starfleet vessels, etc.). It was also this change in Klingon rule that led to the alliance with Romulus in 2267, resulting in an exchange of technologies (including the Klingons getting cloaking technologies) and the sale of Klingon warships to the Romulans (who apparently lacked in large battleships at that time).
At some point, the Empire remade itself once more, returning to the High Council/Emperor-style government rather than the autocratic rule that had gone on for so long. As I am no scholar of Klingon history, I have no idea if this is accurate or not. Wikipedia suggests that the position of Klingon Emperor was restored in 2369, so that's what I'll go with. From a time long before <i>Enterprise</i> until the 24th century, the Klingons were ruled by a High Council consisting of representatives from the Great Houses of Qo'nos.
So my point is simply this: the <i>Enterprise</i>-era Klingons are not particularly friendly towards mankind (perhaps like Italy to the U.S. during WWII had they not joined the Axis), but neither are they an enemy. I'd say that they became especially hostile towards humanity after they made [or perhaps expanded their] contact with the Romulans (another guess: sometime in the mid-23rd century), who got their butts kicked during the Earth-Romulan War 90 years earlier.
I like the Klingons as a neutral species, particularly because they can go either way in a 22nd-century Episode: they can attack for no particular reason or they can rescue the PCs ship from some unfortunate happenstance (like a subspace sinkhole or something).
On an unrelated note: do the Klingons have tractor beam technologies in the mid-22nd century?
On another unrelated note: do the Suliban use cloaking technology that seems advanced for the period (i.e. received from their future contact)?
mactavish out.
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