The article investigates how Australia’s and Poland’s different alliance relationships with the United States influenced their decisions to share the burden in the major warfare coalitions under the leadership of the United States during the twenty-first century. By taking a comprehensive approach to alliance politics, the article examines how four different forms of alliance politics, including risk of abandonment, opportunity for gain, security dependency, and common values, affect burden sharing. It concludes that alliance politics influenced Australia and Poland in very different ways, largely depending on the state’s alliance relationship with the United States.