Naritsugu was reincarnated 30 years after the events of the film in Imperial Germany.
Okay, so let's consider a few facts about Naritsugu. Firstly, he seems like dressing entirely in white. Secondly, whilst he's nearly always calm and polite, he's an amoral, psychopathic Complete Monster. Thirdly, over the course of film, he develops an interest in war. The logical conclusion of this? 30 years after his death at the hands of Shinzaemon, Lord Naritsugu is reincarnated in Imperial Germany, just as WW 1 is getting going. A couple of decades later, he joins the Nazi Party, and more specifically the S.S., where he rises to the rank of Sturmbannführer - or, in English, Major. He then gets an order from Adolf Hitler himself to start work on creating artificial vampires, and, well... let's just say that, eventually, he gets all the war he could desire.