Each particular Church is “catholic”
832 “The Church of Christ is really present in all legitimately organized local groups of the faithful, which, in so far as they are united to their pastors, are also quite appropriately called Churches in the New Testament…. In them the faithful are gathered together through the preaching of the Gospel of Christ, and the mystery of the Lord’s Supper is celebrated…. In these communities, though they may often be small and poor, or existing in the diaspora, Christ is present, through whose power and influence the One, Holy, Catholic, and Apostolic Church is constituted.” [LG 26] [814, 811]
833 The phrase “particular church,” which is the first of all the diocese (or eparchy), refers to a community of the Christian faithful in communion of faith and sacraments with their bishop ordained in apostolic succession. [Cf. CD 11; CIC, cann. 368-369; CCEO, cann. 177,1; 178; 311,1; 312] These particular Churches “are constituted after the model of the universal Church; it is in these and formed out of them that the one and unique Catholic Church exists.” [LG 23] 
834 Particular Churches are fully catholic through their communion with one of them, the Church of Rome “which presides in charity.” [St. Ignatius Of Antioch, Ad Rom. 1, 1: Apostolic Fathers, II/2, 192; cf. LG 13] “For with this church, by reason of its pre-eminence, the whole Church, that is the faithful everywhere, must necessarily be in accord.” [St. Irenaeus, Adv. haeres. 3, 3, 2: PG 7/1, 849; Cf. Vatican Council I DS 3057.] Indeed, “from the incarnate Word’s descent to us, all Christian churches everywhere have held and hold the great Church that is here [at Rome] to be their only basis and foundation since, according to the Savior’s promise, the gates of hell have never prevailed against her.” [St. Maximus the Confessor, Opuscula theo.: PG 91 137-140][882, 1369]
835 “Let us be very careful not to conceive of the universal Church as the simple sum, or… the more or less anomalous federation of essentially different particular churches. In the mind of the Lord the Church is universal by vocation and mission, but when she pub down her roots in a variety of cultural, social, and human terrains, she takes on different external expressions and appearances in each part of the world.” [Paul VI, EN 62] The rich variety of ecclesiastical disciplines, liturgical rites, and theological and spiritual heritages proper to the local churches “unified in a common effort, shows all the more resplendently the catholicity of the undivided Church.” [LG 23] 
It is under the spiritual leadership of the Bishop of Rome, commonly known as “the pope,” that the church is united in one body of knowledge, understanding, and mission by the power invested on St. Peter by the laying on of the hands of Christ himself and the Holy Spirit who works through the hands of St. Peter and his successors.
Christian division has been a reality since the first century of the Church’s founding. Christ’s prayer: That all may be one . . . so the world may believe. (John 17:18) must respect the free will of those not united in the Body of Christ in other faith traditions.
Source: Catechism of the Catholic Church para. 751-752, 830-835.