MC asked how the old world fall.
Shopkeeper answered.
1. The Case of America
Sole Super Power America got a new president, Bush who wanted to be a war hero, so he made up some threat so that America needed to be saved, and attacked Iraq and destabilised the region (later giving birth to ISIS, etc), upgrading the region's threat from hostile territory to unstable region with sources of constant malicious attacks (terrorist's actions) and degrading America from Sole Super Power lording over all countries into a Country under Constant Threat, always insecure.
Next Negative Campaign president was Trump, while America was still number one in a lot of area, he used the external threat and other insecurities to promote the idea that America is no longer great to launch his campaign of Making America Great Again. In effect the MAGA campaign changed general consciousness of Americans from America Number One to America No Longer Great, lowering the expectations and what was standards from before the campaign.
Americans found the Negative Campaigns as an effective way for presidency and used it further, so more and more negative campaigns destabilised the country.
2. Internal Use of the Strategy of Using External Foes to Unify the Country
Bickering internals united under a single banner to fight external threat. Using the threat of external enemy results in solidifying the grip on power and distracts nationalists' watch on internal problems and turns them to passionate followers against external threat. A very effective strategy. Until it was used internally to solidifying factional powers against other factions.
Factional use of the strategy turned factional bickering to straight hostilities, and factional struggle for power turned into civil wars. The strategy instill solidarities and comraderie internally AND sense of threat and hostilities agaist an external enemy, so when it was done factionally, said faction no longer see other factions as fellow nationals but foreign enemy.
Using this strategy is like turning on IFF functions in a group of humans, turning the group one belongs to as friend and other group as foe before ducking out in combat. While using the strategy against foreign enemy may be useful in obtain power without directing real combat against said foreign enemy - the enemy is far away, and combat logistic is a real b1tch so no real war while diplomacy getting in the way, so it merely accelerated hostilisties, and when it was done internally against factional enemy, the enemy lives next door without logistic problem or intefering diplomacy, and combat is inevitable.
Using the strategy internally is like turning on IFF against one another, in effect turned friend into foe. The result was neighbours killed each others, civil wars erupted and the country split.
3. War Hero Wannabe in Peaceful Country
No War No War Hero, so Hero Wannabe needed war to complete themselves.
American case:
Alright, Bush Sr. and Jr. have their reason to invade Iraq, and 9/11 is a suicidal attack with a lot of hate against America, while Saddam, Al Qaeda and ISIS are b@st@rds, acknowledged. But the wars still reeks of looking for enemy to gain popular support internally against external foe to me, while "war president" and "axis of evil" sounds like delusion from hero complex. As for Trump, he capitalised the insecurities American felt to launch a negative campaign that internalise the feeling of "America no longer great" to support his campaign of "Making America Great Again". Well, although I'm not American I fail to see what his campaign and his antics done on the "greatness" of America. If anything it seems like making Americans get used to mediocrity.
Other cases:
From what I read on Bali Bombings case, the convicts seems enamored of the idea fighting holy war and but unwilling to go where Islamic countries suffering wars and instead tried to have war comes to Indonesia so that they can have their holy war. There were also some religion based conflicts in some areas as well, inciting neighbours to kill neighbours for religion differences by way of solidarity and brotherhood amongst believers by negative propaganda (telling stories (true and untrue) of injustices and cruel acts that fellow believers suffered under the hand of the other religion's believers) and the call to protect and revenge.
Flaws:
1. Internal Use
Turning factional (racial, tribal, religions, etc) conflict into bitter hostilities by festering solidarity and brotherhood with flat-out hostility against the other party is recipe for separation and breaking up.
2. When the enemy is gone
Case of Witch Hunt, Salem:
It appears to me that the religious society of Salem was united with the help of fear and hostility against an external enemy: the witches. And when it comes to them that the witches are not real but imaginery enemy, the society lost its pillar: the unity against the enemy since the enemy is not even real. The Witch Hunt mass histeria is the result when a society needed an enemy to function, and when there's no enemy they desperately seeks (hunts) the enemy so that the society and its people can keep functioning.
Case of Indonesia:
This is my personal opinion, but it seems that the first president Sukarno and the second Suharto both uses two pillars, one internal and another external to cement their power. Sukarno's internal pillar was communism while his external was anti-colonialism. Sukarno rise to power by fighting wars against colonials to gain Indonesia's independence and he depended on communism to create his ideal nation. Communism failed to fulfill its promise while creating troubles with religions because of its atheistic ideology while by 1960s colonialism was gone and UN rise above nations and stipulates equality for all. So he got troublemaker instead of problem solver for his internal problems and no enemy to deflect people's attention to internal problems. Without support his power crumbles.
Suharto rises to power using communist problem and slaughter them, uniting Indonesia against national enemy: the communist. For three decades he dedicated internal attention to developing the country with some good results. But by the 1990s communism has fallen and communist countries fallen apart, so no enemy to focus people's attention. Afterward, economic crisis torn Indonesia's economy apart, and his power crumbles as well.
The problem: Dependency on enemy, when the enemy is gone, you're gone too.
3. Use in Time of Peace
Negative campaigns seems like strategy that should only be used in time of war. It's like imposing martial law, cutting civilian benefits and turning it into war effort against external enemy, or you could say cutting one's own flesh to break enemy's bones.
Using it in time of peace to gain the seat of power is weakening and destabilise civilian base, people no longer care about internal problem and instead looking externally for enemy. Just see Trump.
Not much historical research was done for this, so take my opinion with grains of salt.
Anyway, the main point was to create the reason for the fall of the world and the nuclear war that follows, and my background story is this: Many rises to the seat of power by raising hostilities against external enemies so that international relationship broke down, while others tried to gain power by igniting hostilities against other factions in their own countries so the country fall apart. The hostilies remained unsolved until a madman press the button.