Thank you for your response. On re-reading, I have decided that I did not adequately separate out the intents in that sentence, and so I have rewritten that section as, "or obtain control of the territory through short-term or long-term demographic change."
Is a country of 1 billion sending 6 million guys to live in a neighboring country of 5 million and vote for annexation a "war"?
Since no one attempted to shoot or bomb anyone, but the original inhabitants were pushed below the majority of representation and thereby lost political control of the territory, it could be called "a form of conquest other than war."
If it's a paid operation it's kinda war-ish, but official permission and lack of casualties separate it.
Regarding the rest, the actions of existing actors are tuned according to the existing conditions.
Governments do appear to leverage their ethnic diasporas for political ends, although these appear to be mostly first or second generation immigrants. This poses less of a challenge for moderate immigration than it does for high immigration. (Documenting examples and extent would be a good research topic if I ever do a formal write-up.)
Ethnicities are not unified rational actors, although they are potential fault lines. Ethnic bloc voting, ethnic favoritism, and ethnic riots are still issues.
A government is a power structure - and I have heard reports that some have tried to get more influence over their diasporas, meaning that diaspora behavior isn't solely about loyalty. Certain family structures, rules, or organizations may also be power structures or support them, causing greater synchronization/alignment of behavior.
My concern is that while Argumate is an atheist, I don't feel he has adequately addressed how to weaken these structures.
With borders, a high-fertility, high power structure strategy is less effective. You still have to do the war.
If you can take over territory by making more voters and keeping them loyal, without a war, this changes the meta - not for groups as unified rational actors, but for human leaders and for people embedded in the matrix of those power structures.
Poi just posted something completely unsourced, so I cannot say whether it's real or not, but I can use it illustratively. We'll say it's a hypothetical example.
The move of only hiring Indians turns the company into an ethnicity-related power structure where someone in the network could be rewarded for showing ethnic loyalty, or punished for not showing ethnic loyalty. This would be enforced socially.
There is always an incentive in politics to defect and loot the commons. Just... in general. Right does it. Left does it. Race and ethnicity are pretty powerful points of coordination, because they're often visible, and people can't quit being a member of their race, nor can people aside from the intended recipients of a transfer join the group in order to receive the transfer.
Since the resources of each individual (including time and energy) are limited, each individual then faces a choice - do they invest in the central government, and race/ethnicity-neutral policy, or do they invest in alternative ethnicity-based power structures?
If the authority of the central government erodes, then its provision of services will no longer be reliable. When an alternative ethnicity-based power structure or network of power structures is just starting up, its benefits will also be limited or not reliable. However, as the level of investment increases, the level of provisioning it can provide - and the bid it can make for supporters - will also increase.
If the central governments are weak everywhere, due to inter-group fighting causing underinvestment in the commons, then ethnicity-based alternative power structures might provide more reliable insurance and security services. Legitimate businesses can't necessarily act as an alternative, as it is the political environment which allows them to exist.
In this way, an equilibrium could be reached where ethnicity is dominant even if the median person doesn't have a high baseline level of ethnic attachment, due to the shift in material incentives.
(It is my belief that there is a natural core of people who have high baseline ethnicity/ethnicity-like attachment, and a range from low to high, so it doesn't ever entirely go away, but it can be weakened or change form.)
While this outcome is not guaranteed, I feel that it is an under-considered risk in open borders discussions.
With a higher level of friction from regular borders with limited immigration, immigrants will have longer to marry into the host country, thereby making the people harmed by the looting of the commons their own children and grandchildren, while not having the insulation of an ethnicity-based alternative power structure to protect them, due to norms acting on individuals to prevent the formation of such structures while they are still politically weak.