system
Given the following post, respond as if you're commenting on Reddit:
human
[Under the Dome] What would've happened if the dome had erupted on a more populated city like New York, Beijing or Moscow?

What would the general populace's reaction be? Would governments consider this a new type of weapon?
gpt
With such a large population, and also such an enormous amount of space, things would be very different.

First of, things would probably remain calm for the first couple hours or even days. People would need time to process what is going on, transfixed on the dome.

Some would stay inside for a while, some might try to find a way out anyways. All major roads leading to the outside world would be swamped with a perpetual traffic jam as people tried leaving that route anyways, not realising how futile driving up to an impenetrable wall is. Other might try to tunnel out or blast their way through.  That's also the point where word of mouth spreads and the people truly realise that they're trapped.

This phase might take days or it might take weeks/months depending on how well the local government and other bodies manage to maintain the order. Either way, expect to see a spike in crime as people realise they are trapped and metropolitan areas like this rarely have their own food supply, instead relying on imports. 

After that point, expect martial law and much much rougher times for a long time. Setting up things like a steady food supply will take a while in even the best sircumstances. Expect people to split off from society and governing bodies to begin their own micro states within the dome. These micro states might be friendly or hostile to each other. In a way this is random, it all depends on the way they split off and the governments reaction to that. This fragmentation is also necessary, i highly doubt that the local govt can control the population adequately with just it's police force. They'd still be a major player, but they can't spread themselves too thin.

This period would see a lot of die off, especially in the later stages. Violence and crime would take a portion, but most of those perished will be taken by starvation or untreatable diseases. It's hard to put a number or percentage on this die off, but expect it to be incredibly significant. Think about it like Stalingrad, except there is no way out and no supply line for either sides. And now there are dozens of them. 

At the end of this period the die off will slow down as the population reaches a more or less sustainable level again. Any surviving micro states will logically have set up a food source and makeshift economy, possibly by trading with other states. Life within those states is rough, but mostly resembles the culture before the dome. unoccupied territories outside of micro state land will be much much rougher and wilder. The states won't have the resources to control them, and as such a sort of dead mans land exists between states.

Various loners, groups or even tribal like entities probably live in this dead mans land, competing with eachother and the states for food and resources. While the states probably work together to some extent, these other entities are smaller and much more likely to be thieves or even raiders. Micro states will probably maintain their borders fiercely for that reason, and trade caravans will be armed. It's likely that this divide will cause resentment on both sides after a while, possibly ending in conflict.

As time goes on and the micro states solidify their local power, they'd probably start competing with eachother aswell. Don't expect all out war, but skirmishes and quick coups are likely. Eventually only the most powerful states will remain. Any dead mans land tribes left at this point will pick sides, be absorbed or entirely cease to exist. 

At that point you either get multiple large states of roughly equal size and power, forever stuck in a status quo or one giant state. Either way, it is likely that things will conglomerate en you'll end up with one big entity focused on food production and surviving within the dome. I'd say wars are less likely due to renewed food stocks, unless some significant event takes place. An enormous loss of crop, some kind of hostile action or completely incompatible states.