This question ended up being far more difficult than I expected, and it's what would ultimately shape this story more than anything else.
At first, I thought of what most of us already had in mind: Dracula awakens, more powerful than ever, and unleashes a demonic army to destroy all of humanity. But the problem was that it's not a particularly original, or, let's face it, interesting idea. Every attempt I made at imagining "demonic war" funneled into some awful ending scenario with a generic monster army spilling out of a castle under assault by a crazy military setup - and that wasn't an idea I was very fond of. Not only did it sound impossibly cheesy, but it also kind of threw the Belmonts out of the picture - there wasn't much space left for one legendary family's struggle against Dracula if his castle was also getting flooded by tanks and paratrooper squads. There were too many things to consider, too many artificial plot points I had to invent for a story that barely made any sense in the first place.
To give you an idea, here's a pretty accurate account of my early thought process. If anything, just read it for the laughs:
"So who does the military belong to? The Church? Probably not. The state of Transylvania? But why only them? How about Europe, then? The entire world? That's too much to worry about. Maybe a secret order that for some reason is the only one to know about Dracula? And that somehow manages to assemble a massive private army to stop him?
What kind of weapons would they bring, anyways? Tanks? Aircraft? Missile Launchers? Anything to bring down Dracula, right? So while they're at it, why don't they just go about obliterating zombies and axe armors with drones and orbital missiles... But then maybe Dracula's Castle is a "creature of pure chaos", so it can get a special magical anti-orbital-missile-force-field...
And what is Julius supposed to do in all this? Is he getting hired by the Church? How about by the government? Maybe he's going to lead the army? Maybe some real-time-strategy? But we want a 'lone Belmont'. So maybe he's just going to be the "super special Dracula assassin" to be parachuted in from a helicopter. Heh. Someone, of course, is going to tell him: "you're our very last hope to end this war". Always someone intimidating enough who can speak with a deep and serious voice. Like the Prime Minister. Or the Pope."
So after obsessing about it for a few more days, and failing to come up with a scenario any more compelling than "kill them because they're monsters" (and some cool vocal impressions of the Pope), I tried to take a different approach. After a while, here's what I came up with:
Since Dracula and modern war were best kept separate, I decided that this war would be one waged by men against men. There are several reasons why I chose to do this. First of all, I'm convinced that Aria's 'Demon Castle War' is more a thematic indication than it is a literal description. It's also probably the product of a less-than-perfect translation, to be understood in context and not really word-for-word: kind of like how Akumajo Dracula, had it not been given its Westernized namesake, would've been literally translated as 'Demon Castle Dracula'. So what I decided to do was to strip it down to its most basic meaning as a "Castlevanian war", a war that was somehow crucially tied to or under Dracula's influence, but that didn't necessarily have to involve him directly. Second of all, I felt it was a waste to reduce all of the complex premises of an actual conflict to another "evil monster" war -- we've already seen so many zombies getting whipped to death in the series that letting the military jump into the mix for no particular reason felt like unnecessary bloat. There's so much more to exploit, and so much more to build, if I can create a war driven by human decisions and with entirely human consequences.
But this choice also meant something that I originally hadn't planned to do: the Demon Castle War no longer stood at the forefront of the story. And I realized that for my own purposes, that was acually a good thing. This was Castlevania - a series about the Belmont family's struggle against Dracula - and as much as I wanted to shape this narrative into something thought-provoking and poignant, I didn't want a massive war clouding up the core story I wanted to tell. So I made my choice. And in that moment, my 1999 scenario was born.
I was all set, and all I had to do was throw the Castlevanian element in. So to pull it all together, I imagined a modern world under the influence of Dracula's Curse.
The land becomes infertile; nature grows restless as it warps, withers and dies; a lingering darkness falls as men grow fearful, cruel, and selfish; and none, not even the dead, can find peace. Under the strain of dwindling natural resources, those in power become greedy and belligerent; corruption runs rampant; authoritarian and expansionist ideologies are on the rise, and the shadow of war looms in the horizon.
There you have it - that's the "catalyst" for my Demon Castle War. I'd gotten the causes down - now, for the actual motives.
Once again, I dove deeply into international intrigue, trying to come up with some crafty sociopolitical implications. But then I realized something: my story was getting far too complicated. I had already come to the conclusion that this story's spotlight would be squarely set on Julius -- and yet here I was wondering about something like how the United States would handle diplomatic relations with a war-torn Europe. So here was my idea: I wouldn't give specific motives for this war. Of course, the war was always going to be given vague political or economic rationales, but since Julius would never truly going to be involved in it, and since it was always going to be entirely separate from the main narrative, I decided not to add another loose thread - which really wouldn't have gone anywhere - in a story that I felt most needed focus. This actually ended up playing in my favor - I began to understand that the more obscure this war was, the less invested we were in its motives, the more inexplicable its very existence would seem, and the more pathos I could reasonably draw from it. Julius' role, in this case, is one of a passive observer: he runs into a conflict that isn't his and sees atrocities committed for reasons he doesn't entirely understand. In fact, those fighting in it themselves will begin to lose sight of the motives behind their own hostility. This plays well in a variety of themes I'll be developing later on; and it also gives the narrative an apocalyptic dimension, which was very much what I was aiming for, in context.
Now, for exactly the same reason, I've decided not to name the country or the nation this is happening in. I didn't want to have to worry about state politics, borders, or nationalities in a story which never really warranted it. And the lack of a defined nation as the setting gives this setting a sense of scale that it wouldn't otherwise be able to attain, while allowing Julius' journey to have a true sense of continuity.
The backdrop for Julius' journey, then, is an apocalyptic depiction of a collapsing society on the brink of war, plagued with internal unrest and crumbling under the strain of external conflict. By design, it's an unobtrusive and fully independent setting, running parallel to Julius' own quest and motives, but always endowed with enough weight and presence to exert a significant influence in shaping characters and events. It's a dynamic environment that quickly evolves from visible tension to escalating hostility, and also one that easily stands out from any generic modern setting.