As Donald Trump has won the high-stakes US presidential election, sweeping changes are expected to affect South Korea in fields including economy, trade, security, defense and inter-Korean relations.

While Trump’s slogan, “Make America Great Again,” resonated among the majority of US voters, his core stance -- “America First” -- is likely to force many countries, including South Korea, to confront drastic challenges and costly decisions in their relations with the US.

Amid widespread concerns, President Yoon Suk Yeol held a phone call with President-elect Trump on Thursday to congratulate him, and they agreed to hold an in-person meeting at an early date, according to the presidential office.

During the call, Yoon expressed hopes for continued cooperation between the two countries under Trump’s leadership and briefly shared views on security, economy and other issues.

There are already a torrent of suggestions about what South Korea should do to grapple with potentially difficult issues related to Trump's second term. Despite different details, experts generally agree that Korea needs to reformulate strategies on diplomacy, security and international trade in connection with the US.

The need for advance preparations is greater than ever in consideration of the imminent impact. Some experts even floated the idea that the Yoon administration has to tap into the pool of former public officials who had been in charge of negotiations over security and trade during the first term of Trump to set up a new group better suited to his “America First” policies.

First and foremost, once Trump officially makes his way to the White House, he is widely expected to push South Korea -- a nation that he described as a “money machine” -- to pay far more for the defense cost-sharing scheme. Last month, Trump said Korea would be paying $10 billion a year for the stationing of US Forces Korea if he were to win the presidential race.

Now that Trump has won the election, he could demand the renegotiation of the recent defense cost-sharing deal between Seoul and Washington, under which Seoul pledged to pay 1.52 trillion won ($1.08 billion) in 2026.

Uncertainty lingers over how Trump will handle the issue regarding North Korea, which continues to engage in provocative activities including the test launch of long-range ballistic missiles. One probable scenario is that Trump resorts to his personal diplomacy with North Korean leader Kim Jong-un, but there is a possibility that Trump will not give high priority to North Korea-related issues, at least in the early stages of his second term.

Another change that Trump will bring about involves the economy and trade. Already, the South Korean won tumbled against the US dollar Wednesday on the news that Trump won reelection, signaling a significant change that export-oriented companies will face.

Experts forecast the value of the South Korean currency to weaken further in the coming months as trade relations between South Korea and the US could undergo a wave of changes. Last month, Trump vowed to impose a minimum tariff of 10 percent, and up to 20 percent, on all imported goods, raising tariffs on imports from China to as high as 60 percent.

For the export-driven South Korean economy, such protectionist policies can translate into higher uncertainties in trade policy and market volatility. Finance Minister Choi Sang-mok on Thursday said a second Donald Trump presidency is expected to have a “considerable impact” on the South Korean economy. He said the government would devise swift responses to major policy changes and market turbulence.

Given the gravity of the forthcoming changes, South Korea must set up more proactive policy measures to address the major challenges that Trump will bring about.