Comprising of here nine states, EU9 has grown to be an essential component of the European Union (EU). This entity became part of the EU in its 3rd expansion phase in 2004, bringing diversity and fresh perspectives into the Union's mix.

The EU9 countries include Poland, Lithuania, Latvia, Hungary, Czech Republic, Slovakia, Slovenia, Estonia, and Malta. These countries each have given meaningful efforts towards broadening the objectives of the European Union.

Therefore, comprehending the responsibility EU9 holds in the European Union is required for any study relating to European economics, politics, or international relations.

From their entry, the EU9 countries have contributed substantially towards shaping the European Union's policies. Their geographical location offers critical strategic edges, making them a vital part of the EU's defense and security strategies.

Additionally, these nations have significantly contributed to the European Union's economic and financial strength. The EU9 nations' rapid economic development and keen integration into the European market has led to heightened trade with other EU states.

The cultural contribution of the EU9 is also significant. These states introduce profound historical backgrounds, individual cultural practices, and assorted languages, therefore enhancing the variety of the EU.

The inclusion of EU9 has also affected the internal politics within the EU. With their involvement, the power dynamics have changed, with new coalitions and alliances forming.

In conclusion, the roles played by the EU9 nations are significant. From economic influence to cultural richness, and from security strategies to political dynamics, EU9 has fortified the European Union's structure. As such, an thorough understanding of the EU9 is vital to fully grasping the intricacies of the European Union.