No one wants a war with North Korea. A war on the Korean peninsula is hugely dangerous due to the close proximity of Seoul, a mega city with a population greater than New York, to a massive amount of North Korea artillery (Seoul is less than 40 miles from the North Korean border), as well as the close proximity to China (which considers the Korean peninsula to be firmly within the realm of their national interest). Any military action has the potential to lead to ten of thousands of civilian deaths, and to spiral out-of-control leading to a possible war with China (and possibly Russia). Of course, doing nothing and allowing North Korea to develop a nuclear weapons program could also have similar consequences. It depends on how much you trust Kim Jong-un to be an honorable world citizen after getting a nuclear program.
Will there be war on the Korean peninsula at some point? If so, when? I don't know, but over the long-term I think it is more likely than not that events will lead to military confrontation at some point. As to when: I don't expect anything to happen until after the Winter Olympics are held in South Korea this February. So, any time after February is my guess. There is still time to prepare for a worst-case scenario (while praying for the best-case).
Here are a few recommendations on what to do:
1) Bring home any family members that are overseas. If a world war should break out, or nuclear weapons be used even in a limited way, it may be months or even years before you will be able to reunite with family members who are overseas when hostilities break out. Bring home NOW any students studying abroad, or any other family members who are overseas for whatever reasons. Cancel any overseas vacations or trips for 2018. You can always go later if nothing happens.
2) Newbies: Start preparing now, if you haven't already. You have to to prepare, but get started soon. Don't know where to begin? Read my article A quick, no frills, down & dirty guide to preparing for the End, which will give you the basic outline, in less then 10 minutes, of what you need to be doing.
Another good resource for general preparedness and survival is James Wesley Rawles' book How to Survive the End of the World as We Know It: Tactics, Techniques, and Technologies for Uncertain Times.
3) Advanced Preppers/Survivalists: The 1987 edition of Cresson H. Kearny's Nuclear War Survival Skills is available for FREE download at http://www.oism.org/nwss/. I list this as being "advanced" because folks need to be doing the basics of prepping first, before trying to prepare specifically for a nuclear war.
In Chapter 13, Kearny gives a list of minimum preparations, including shelter, ventilation-cooling, water, fallout meter, food, sanitation, medicines, light, radio, and other essentials. You can read chapter 16 on my website, or preferably download the entire book for free from the above mentioned link.
4) Are you living in or near a likely nuclear target? For a variety of reasons, all-out nuclear war is extremely unlikely even if events spiral out-of-control and into World War III, but the limited use of nukes is a possibility. Carefully consider where you are living, and if there are any critical economic, political, or military targets nearby. Consider moving if you are near one.
5) Food and Water will be critical. You need to have plenty of stored food & water, and ideally the ability to produce even more. Our modern food distribution system is precariously balanced, and will likely collapse during and following a major world war.
6) Dealing with Radiation: Kearny's Nuclear War Survival Skills (link to a FREE download is given above) goes into much more detail, and with more expertise, than I can give here, so I'll only make a couple of quick comments:
a) The best protection against radiation is space and mass. The further way from a nuclear blast you are, the safer you'll be. The more mass you have between you and a nuclear blast, the safer you'll be.
b) Potassium Iodide Tablets offer some protection (not complete radiation protection), but you need to know how to use them properly. Find out now how to use them, and ONLY use them when absolutely necessary. Start with the CDC video Pharmaceutical Countermeasures for Radiation Emergencies – KI (Potassium Iodide).
c) Dr. Joe and Amy Alton's excellent book, The Survival Medicine Handbook, has a chapter on Radiation Sickness. I HIGHLY recommend this book, and consider it a MUST HAVE for any serious prepper or survivalist.