The Age of Isolationism was a moderately obscure time period in the Classical Era, starting with Darshi Yaun's rise to power. Because of the autarkic efforts pursued by her, and the closing of Ravennan markets for a temporary period of time, most sources of cash crops like tobacco, cocoa, or even plants like cotton, which was used by aristocrats and other rich and influential figures, upsetting those at the top. This also put a noticeable dent in most countries food supplies, meaning that rationing measures was put into effect. This caused a tidal wave across the relatively fragile economy of the world ever since the end of the Age of Frost, and causing economic recessions all across the world. While pressure was put on Aisling by foreign powers, she refused to comply, and the rest of the world was left stranded. Because of this, many other nations also pursued economic independence, and to also stay out of other's affairs, as this was seen by many to be the reason why Aisling closed off to the world, and as such, the Age of Isolationism began.
Most notably affected by this sudden change was Uthan. They were known was the international trade hub of the world, and with nobody trading with their international partners as often as before, their income suffered, and they nearly underwent a political and social crisis. Luckily for everyone who didn't want a civil war in the most important geographical location in the world, the Lord Protector and the Concilium managed to reach a consensus with the numerous different angry groups of people inside Uthan and avoid a full on peasant revolt or coup, but their centralized power was extremely diminished because of this crisis, allowing The Blood Mages to further infiltrate the government and to allow them to further take control of the state.
The Eari, who were already isolationist to begin with, wasn't very affected by the lessening of trade with other countries, and continued their business as usual, lightly trading with coastal villages and a few dockyards.
The Republic of Valdar and Kingdom of Falglor weren't very affected by this age, other than what was said in the first paragraph. They suffered economic blows, and because of that, focused on domestic industry and production. Also because of this, Falglor found out about their absolute dependence on The Order for ores and precious metals, further growing their disdain for the organization, even more so as they found out they couldn't mine more ore for themselves because the Order owned the legal rights for the area where the metals were more plentiful, leaving Falglor either dependent on trade or forcing them to mine away at piles of rock with little to no gain from it. The Order were also subsistent upon Falglor for them to process their metals and ores in order for them to even hope to make a profit, made sure that the Age of Isolationism caused their influence to fall extremely.
Another nation that was highly affected by this was The Yunnaiteddo Federation. Already separate from the rest of the world, the western clans, who were concerned about the power the east were accumulating through their deals with foreigners, gladly took this chance to strong arm the east into isolationism and diminishing their power over the federation. This wasn't exactly a move fueled by economics, but a political reason. Because of this, when the Age of Isolationism finally came to an end after Aisling fell from power and the more susceptible Umhen became king, the leaders of Valdar, Falglor, Uthan, and the Order were able pressure him to reopen Ravennan markets, Yunnaiteddo remained isolationist until the late 600s, when The Holy Imperium of Moneeri were knocking on their door.