In the 2015 Singapore general election, Lee was re-elected in Ang Mo Kio GRC, with the PAP winning 83 of 89 seats in Parliament and 69.9% of the national vote. Lee's fourth term as prime minister was marked by events such as the China–United States trade war, which adversely affected the nation's economy, being highly reliant on free markets and trade. Increased cyberattacks on Singapore-related services and websites led to the introduction of the Cybersecurity Act in 2018 and the establishment of the Cyber Security Agency. The defeat of the Barisan Nasional government in the 2018 Malaysian general election, which saw the return of Mahathir Mohamed as prime minister, led to a chill in relations as the new Pakatan Harapan government sought to overturn previously signed agreements on the Kuala Lumpur-Singapore high-speed rail and Johor Bahru-Singapore Rapid Transit System, and also disputed with Singapore on airspace and maritime rights. As part of the Lee government's effort to promote Singapore as an international center for arbitration, the city hosted the leaders of Mainland China and Taiwan for the Ma-Xi meeting on 7 November 2015 and the North Korea–United States summit on 12 June 2018. Singapore hosted the signing of the Singapore Convention on Mediation on 7 August 2019, the first United Nations treaty named after it, and ratified it on 25 February 2020.