Lets pick the opponents for the next World War. It would involve either Russia or China, and one or more of their client states. No other countries have the power or clout to rally other states around a world war. If it doesn't involve them, it's not a world war. Secondly, it would likely involve Nuclear, Biological or Chemical attacks. Nothing else (except perhaps a blockade of the Straits of Hormuz) has the power to compel numerous nations into war. Even an invasion of Taiwan would be a regional response. So, the field is narrowed to states with NBC capability who can either blockade the Straits, or use nuclear weapons. The field is therefore narrowed to Iran and North Korea, with Pakistan and perhaps India a second remote possibility. Thirdly, the outcome for scenarios that have been war-gamed at the NWC are uniformly difficult to predict. First use of a nuclear bomb can either involve a massive nuclear retaliation, or a targeted limited conventional response. In either case, the first strike will be traced to the nuclear source (the nuclear signature of each reactor is known, and the origin of nuclear material is traced using forensic science). No state actor can sell to or use a terrorist organization to deliver a device without leaving evidence of the bomb's DNA. If its North Korea, the South Korean and Japanese and perhaps Australia, Philippines and Taiwan would be called in (perhaps ASEAN). If its Iran, I suspect Israel, Europe and perhaps a few gulf states would be allies.
Depends on the circumstances. The US favoured Israel over the native Palestinians and provoked all the Arab states. This brought a lot of hate on the US. Israel is determined to be a Jewish-dominated state even if non Jews are the majority. This is undemocratic and caused the present fracture of West Bank and Gaza.