Vast majority? The combined market cap of those four companies is maybe $500-600 billion combined. The total S&P 500 market cap is roughly $45-50 trillion. So

Vast majority? The combined market cap of those four companies is maybe $500-600 billion combined. The total S&P 500 market cap is roughly $45-50 trillion. So defense contractors represent maybe 1-1.5% of a typical index fund portfolio.