If any day our world is attacked by a very hostile but intelligent creatures from outer space, are we prepared?

Scientists say that there are enormous possibility that there are many intelligent civilisations outside there in the infinite space. Some are even more intelligent than human beings. This thing has not been proved, but they think that it is a bright possibility. But we the people of earth are fighting with each other, and are preparing our arms and ammunition against each enemy country. But are we really prepared to fight back in such an eventuality which I have mentioned above? It seems, we are not at all prepared for this possibility which even the scientists imagine as a possibility. So, it seems that we deny this possibility as "fables" or "children's imagination". Isn't it? What do you think? Should there be an international collective strategy among nations to fight back together in case such an eventuality becomes true.