The paper examines a two-stage conflict game between two groups of players. In the first stage, each player independently selects how much monetary effort to allocate toward defending themselves. The second stage involves players deciding how much effort to spend on attacking players in the opposing group. Success probabilities are determined using probabilistic contest success functions (CSFs), which account for the effectiveness of attackers and defenders. Player heterogeneity plays a crucial role, as differences in resource usage and effectiveness significantly impact strategic decisions and equilibrium outcomes. For instance, variations in effectiveness influence which players actively participate in attacks and which rely on their allies. The outcome of this strategic interaction ranges from full-scale conflict to complete peace. A numerical measure of efficacy is introduced to quantify these dynamics. When effort costs are linear, the most efficacious attacker leads the attack while allies free-ride on their efforts. However, convex effort costs mitigate this free-rider problem. The study draws parallels with real-world scenarios, such as the Russo-Ukrainian War and intellectual property disputes within the pharmaceutical industry.