I think the uniting force will be a growing attitude and bent toward eclectism. By this I mean an openness toward accepting elements from any and all religions regardless of the compromising effects. Along with this there is an intolerance for absolutes, at least until the man of lawlessness seeks to rule absolutely and claims that he is god. This was present in the Roman world of the time of Christ and the early church and it has become a prominent issue in both the New Age movement and the eccumenical movement of the past 30 years. These movements are totally intolerant of true biblical Christianity while they open their arms to everything else. A number of New Age leaders like Marilyn Ferguson have specifically spoken about the need to do away with those in the Christian community who are opposed to this eclectic mentality.
Closely tied in here is another common demnominator of this and all Satanic movements. It is the exaltation of man and his ability to save himself and solve his own problems. Society and religion are becoming more and more man centered, government centered, and social centered, rather than Christ centered.