It is very rare for top clubs to miss the competition, although it can happen in exceptional circumstances. Defending holders Manchester United did not enter the 1999–2000 FA Cup, as they were already in the inaugural Club World Championship, with the club stating that entering both tournaments would overload their fixture schedule and make it more difficult to defend their Champions League and Premiership titles. The club claimed that they did not want to devalue the FA Cup by fielding a weaker side. The move benefited United as they received a two-week break and won the 1999–2000 league title by an 18-point margin, although they did not progress past the group stage of the Club World Championship. The withdrawal from the FA Cup, however, drew considerable criticism as this weakened the tournament's prestige and Sir Alex Ferguson later admitted his regret regarding their handling of the situation.
What clubs have missed the competition? 
Manchester United did not enter the 1999–2000 FA Cup,

Spanish colonization commenced on June 15, 1668 with the arrival of Diego Luis de San Vitores and Pedro Calungsod, who established the first Catholic church.:64 The islands were part of the Spanish East Indies governed from the Philippines, which were in turn part of the Viceroyalty of New Spain based in Mexico City. Other reminders of colonial times include the old Governor's Palace in Plaza de España and the Spanish Bridge, both in Hagatña. Guam's Cathedral Dulce Nombre de Maria was formally opened on February 2, 1669, as was the Royal College of San Juan de Letran.:68 Guam, along with the rest of the Mariana and Caroline Islands, were treated as part of Spain's colony in the Philippines. While Guam's Chamorro culture has indigenous roots, the cultures of both Guam and the Northern Marianas have many similarities with Spanish and Mexican culture due to three centuries of Spanish rule.
When did Spanish colonization commence?
June 15, 1668

The court noted that it "is a matter of history that this very practice of establishing governmentally composed prayers for religious services was one of the reasons which caused many of our early colonists to leave England and seek religious freedom in America." The lone dissenter, Justice Potter Stewart, objected to the court's embrace of the "wall of separation" metaphor: "I think that the Court's task, in this as in all areas of constitutional adjudication, is not responsibly aided by the uncritical invocation of metaphors like the "wall of separation," a phrase nowhere to be found in the Constitution."
Stewart pointed out that the phrase "Wall of separation" was nowhere to be found in what?
the Constitution