Nation-sponsored cyberattacks pose a severe threat to national security, targeting critical infrastructure and disrupting essential services. Among the most impactful attacks on South Korea's banking sector and infrastructure was the DarkSeoul cyberattack, believed to have been conducted by North Korea state-sponsored hackers. Using spear phishing, DNS poisoning, and malware, this attack caused widespread disruption across critical systems. This paper presents an in-depth analysis of the DarkSeoul incident, detailing the techniques involved and offering insights and recommendations for the global cybersecurity community. The motivations and strategic objectives behind the attack are examined, as well as South Korea's response and the broader implications for cybersecurity policy. Our analysis highlights key vulnerabilities and underscores the urgency for enhanced defenses against state-sponsored cyber threats. This study emphasizes the necessity for robust national cybersecurity measures to counter such sophisticated attacks effectively.