The invention of rocket technology helped the human race to reach the space. But there is a dual use behind these peaceful intentions: Highly developed missiles also offer access to exertion of power for quiet a long distance around the globe – specially as delivery vehicles for nuclear warheads.
Dual use goods are products and technologies normally used for civilian purposes but which have military applications.
We find the same features applicable on a nuclear power plant which is intended to be used for peaceful production of electricity (safety and sustainability of atomic energy would open another big book by the way). But many types of nuclear plants produce fissile materials as a by product which can be used for atomic weaponry (or terroristic purpose). Equipped with nuclear weapons a state government gets quiet a little bit more involved in international politics and gains a certain security against being attacked easily. A nuclear bomb increases political influence on a international level: Think only of the five nations who command the United Nations Security veto power. Do they have military nuclear capacity? Of course they do.
Currently, there is a lot of diplomatic business going on about the nuclear program of Iran, exactly because of the dual use of nuclear power. Western nations are afraid of a nuclear armed Iran (well too good knowing what deterring device it provides) and try to stop the Iranian nuclear project by international sanctions. Iran on its part insists on its right for civil nuclear power und international surveillance by the IAEA (with alternating will to cooperation) and want get rid of the sanctions paralyzing the economic situation in the country. Iranian president Hassan Rouhani has liven the international political place up, but nevertheless, the dual use of nuclear power surely is a heavy burden for all takers.
For a clear laid-out overview of the Iran Nuclear Program visit the New York Times timeline.