Co-operation as a process of integration of co-operative individuals or groups, is the desirable state in different kinds of systems. One of the factors conducing to co-operation, as postulated in this paper, can be a threat. On all levels of biological and social integration there are a lot of examples in which a threat itself was a very strong mechanism for inducing co-operation. Higher primate and human sociality is the result of deifferent kinds of threats, they had to cope with in their evolutionary past. Yet, to work a threat must have some properties. Because of the 2nd or the 3rd order intentionality apparent in the higher primates and in the man, to induce or sustain the co-operation, the threat does not have to be real, it can be imagined or artificial. The probability of perceiving a threat in a similar way is higher when individuals have the similar outlook of life. We also consider how to increase the probability of co-operation even in the one-move Prisoner's Dilemma (PD) game. In our modified PD game the players are aware of the other player beliefs and they can be warn be the 'demon' about the second step in the game that we introduced in our model. The winners, or the winners, in the case of co-operation, after the 1st step must face with the third factor (a threat) in the 2nd step of the game. This more complicated and closer to the real life situations model shows how the co-operation could be established in a very short time.