What factors led to ethnic tensions between Singapore and Malaysia during their brief union?

Singapore's brief membership in Malaysia was marked by significant tensions stemming from demographic differences - Singapore had a Chinese majority while Malaysia was predominantly Malay. Despite assurances to avoid political interference, Lee's People's Action Party (PAP) and the United Malays National Organization (UMNO) began operating in each other's territories, sparking race riots in Singapore in 1964. UMNO supported affirmative action for Singapore's Malay minority, while Malaysian authorities feared that Lee and the PAP would gain more influence in central Malaysian politics. These ethnic, political, and ideological differences ultimately contributed to their separation.