NU was born in the atmosphere and the culture of pesantren where the doctrine of traditional Islam has been deeply rooted in preserved. The role of K.H. Abdul Wahab Hasbullah (the leader of the Pesantren of Tambakberas, Jombang, East Java) and K.H. Hasyim Asy'ari (the founder of the Pesantren of Tebuireng, Jombang, East Java) were very significant in the process of the establishment of the NU at that time. Because of their important and widespread influences among traditional Muslim people, especially in rural areas, these two leading kyais succeded in preserving and developing the NU. As a result, many other kyais, especially in Java and Madura, joined or established branches of the NU in their regions. The establishment of branches of the NU not only took place in Java and Madura at that time, but also outside Java. By this means, the NU grew strongly not only in Java, but also in other regoins in Indonesia. The symbiotical relations among kiyais (ulama), santris and pesantrens contributed greatly to the significant growth and development of the NU in many regions in

Indonesia.

The NU –through its leading figure K.H. Wahid Hasyim (son of K.H. Hasyim Asy'ari)– played an important role in the reformulation of Pancasila as the basis of the Indonesian State so that Pancasila was accepted by all political streams, religious groups and social organizations in Indonesia. In addition, the NU –together with other nationalist movements– also contributed greatly to the process of preparing for the nation independence; in building of the Indonesian state; and in the war to defend Indonesian independence. Many kyais of the NU took up arms and were involved in the struggle to free Indonesia from the colonial rule. As a result, Indonesia became a new independent and free state. Both K.H. Hasyim Asy'ari and his son K.H. Wahid Hasyim were appointed by the government as National Independence Heroes because of their important role, dedication and contribution to the Indonesian State.

Despite the fact that the NU at that time was completely or purely a socio-religious organization (not a political organization), it felt obliged morally and nationally to struggle against the Dutch colonial rule and taking part in the war to defend the Indonesian independence. For the NU, nationalism and patriotism became part of iman (religion). Therefore, for the NU, nationalism and patriotism or nationality and religiousity could not be separated from the khittah (the spirit of struggle) because the two elements were closely integrated in its fighting spirit and became a prime mover in its struggle to devote itself to achieving the interests of the nation and state.