In our earlier paper, a generalized Dobrushin ergodicity coefficient of Markov operators (acting on abstract state spaces) with respect to a projection P , has been introduced and studied. It turned out that the introduced coefficient was more effective than the usual ergodicity coefficient. In the present work, by means of a left consistent Markov projections and the generalized Dobrushin's ergodicity coefficient, we investigate uniform and weak P -ergodicities of non-homogeneous discrete Markov chains (NDMC) on abstract state spaces. It is easy to show that uniform P -ergodicity implies a weak one, but in general the reverse is not true. Therefore, some conditions are provided together with weak P -ergodicity of NDMC which imply its uniform P -ergodicity. Furthermore, necessary and sufficient conditions are found by means of the Doeblin's condition for the weak P -ergodicity of NDMC. The weak P -ergodicity is also investigated in terms of perturbations. Several perturbative results are obtained which allow us to produce nontrivial examples of uniform and weak P -ergodic NDMC. Moreover, some category results are also obtained. We stress that all obtained results have potential applications in the classical and non-commutative probabilities.MSC : 47A35; 60J10, 28D05