In modern conflicts, Private Military Companies (PMCs) can take on formidable proportions, pouring billions of dollars into black markets and typically outperforming traditional military factions. These visible practices in Yemen, Nigeria, Syria, Ukraine, and Iraq are part of a broader trend of mercenaries, which is becoming increasingly apparent as state actors blur the line between legitimate and illegitimate warfare, especially in the Middle East, Eastern Europe, and Africa. This chapter will analyse two essential functions of PMCs in global wars: how states utilize them for proxy wars to achieve foreign policy objectives and how state diplomacy is mobilised to support PMCs. The chapter offers original insights into the accountability challenges these arrangements present—including their implications for military spending and political accountability in statecraft—by mapping the complex, opaque networks of companies and financial entities through which PMCs operate.