Originally Posted by
Cyke
Well, yeah. The Vietnam War is one example -- yes, the country is intact, but destroying just one city was enough to spur diaspora that still has repercussions today, as reflected in the number of Vietnamese people living in the US, Canada, and France. There are obviously still Vietnamese people living in Vietnam, but the influx of refugees after the war really affected the US.
There are good odds of meeting a 2nd or 3rd gen Vietnamese American and finding out that their family immigrated as part of the refugee crisis of the war. A minority fraction of the population is still enough to be considered a refugee crisis.
Katrina as well is a well documented example of the government's mismanagement of relocation and rescue efforts, leading to other states struggling to take in survivors. Even mighty Texas had issues coordinating survivor intake -- it's not called a refugee crisis only because movement was intra-country, but the logistics would be even more nightmarish if they had to move to a foreign country with a completely different bureaucracy and style of government.
Also, note that in Trek, whenever Earth is threatened rarely does the villain say humanity is at stake, just the planet or Federation leadership. If Earth is destroyed, it's a huge blow to humanity, even though they're spread out over half the galaxy. It's not extinction, but it's a catastrophic and supremely eventful loss of life nonetheless. You can bet that humans would have its own refugee crisis if Earth was destroyed. They can always resettle after losing humanity's home, but again resettling is a major undertaking in response to catastrophe. Humans moving en masse could be seen as threatening to a Federation member world, and we've seen the kind of territory mess when the Maquis renounced Federation membership and encroached on Cardassian space -- and Maquis numbers are way smaller than Earth or Romulus blowing up.
And then there's the logistics and admin challenges that come with relocating the capital -- blowing Earth to stifle Federation leadership won't kill the Federation, but it would severely hamper their capacity and ability to mobilize, and that's why Earth needs protection. The Klingons couldn't handle that burden and that's why they needed the Khitomer Accords when Praxis blew up and damaged Qonos in Star Trek VI. DS9 also states that the Cardassians need this support from the three powers at the end of the show, despite being a nation whose planet survives a genocidal assault.
As we see with the ample Romulan population here, there's still plenty of them but they're not the force they used to be. It would take decades, maybe even centuries, to rebuild to those previous levels, and even then that would leave other powers unchallenged and free to advance.
A planet blowing up is one thing, and is already a refugee crisis at smaller populations. A capital and/or a homeworld blowing up isn't just a refugee crisis (which it is, obviously), but it would upset the balance and relationship of power with other nations, and severely hampers the ability to coordinate rescue, relocation, and resettlement efforts. That's a huge crisis, too. If we lost Washington D.C., other states would step in to help, sure, but you better believe that we would readily accept help from Canada, Mexico, the UK, the EU, etc, and the surrounding states would have to try to absorb the survivors and evacuees, when they already have a tough time absorbing much slower trends of new residents. And while US states and allies try to help, less friendly countries would look to take advantage of this low point.
Plus, logically, no member world or conquered world is likely to have a bigger population (at least of Romulans) than the homeworld. If this happened to Earth, by most implications, Earth still likely has the highest concentration of humans despite all the colonies. Moving 7 billion humans (nevermind any other races) into hundreds of colonies where the max population is in the tens of thousands isn't feasible, and it's not like you can just dump them on a Federation member world like Vulcan, Betazed, and Andoria on a whim overnight without violating their position in the Federation. That takes a crap ton of coordination that would likely take years to sort out.