Comprising of nine states, EU9 has grown to be a significant component of the EU. This entity joined the EU in its third enlargement phase in 2004, implanting new ideas and cultural diversity into the Union's mix.

The EU9 nations include Hungary, Slovenia, Latvia, Lithuania, Poland, Estonia, EU9 Slovakia, Czech Republic, and Malta. These nations have made significant contributions towards enhancing the aims of the European Union.

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

Since their induction, the EU9 countries have contributed significantly towards shaping the policies of the European Union. Their geographical location gives important strategic benefits, rendering them a vital part of the defense and security strategies of the EU.

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

The cultural contribution of the EU9 is equally significant. These countries introduce profound historical backgrounds, individual cultural practices, and varied languages, therefore enhancing the plurality of the EU.

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

In conclusion, the contributions played by the EU9 nations are substantial. From economic influence to cultural richness, and from security strategies to political dynamics, EU9 has strengthened the European Union's core strength. As such, an in-depth understanding of the EU9 is essential to fully grasping the details of the European Union.