The Ottoman Empire has been expanding by method of jihad (in other words, military conquest).
This is the extent of the empire at the beginning of the battle:
Meanwhile, Christendom was divided by the Protestant Reformation.
And dead is all the innocence of anger and surprise,
And Christian killeth Christian in a narrow dusty room,
And Christian dreadeth Christ that hath a newer face of doom.”
On the Christian side we have a strong leader in Don John of Austria, a handsome 24 year-old son of Charles V, Holy Roman Emperor. At his command were 206 galleys, 40,000 oarsmen and sailors, 28,00 soldiers and knights, the thousands of rosaries said by faithful Christians as requested by Pope Pius V, the ministries of the religious and priests who accompanied the fleet, and the entreaties of the hosts of saints and angels in Heaven.
Spies warned Ali Pasha of the Christian advance thus he had time to set up his fleet in a battle line. This fleet was more experienced and stronger than the Christian one. The naval battle began. The galleys fired cannon balls at each other.
The turning of the tide of the Ottoman advance is due to the prayers of the millions of Catholics in Christendom. October 7th, the day the battle took place, is now the feast of Our Lady of the Rosary, and the month of October is the month of the Rosary.
Are we not facing similar battles today, if not even greater ones? Christians are being massacred and exiled from their homes where they have dwelt for nearly 2,000 years in Iraq and Syria by Islamic groups such as ISIS (or Islamic State). Christians in other Islamic countries continue to face anti-Christian laws that prevent them from freely practicing their religion on pain of imprisonment or death. Unlike in the 16th century when Lepanto was fought, these atrocities are met with apathy by the modern Western culture, which is experiencing its own anti-Christian secularization which thinks Christians cannot possibly be persecuted. The overt culture of death advanced by the Islamic State has just as strong a hold in the hearts of Westerners who accept abortion, assisted suicide, euthanasia and other life-denying practices such as contraception that continues to cause populations of developed countries to plummet to the point where future generations will collapse under the weight of the much larger older generations. Christianity itself continues to suffer from splintering and a lack of unity of believers. The odds seem to be overwhelmingly against the Church.
But we are the Church Militant. We are united as members of the Body of Christ. We are the Catholic Church. Just as 500 years ago Christians united in prayer to defeat the Ottomans, we can unite in prayer now to combat the spiritual and physical evils in our world today.
To read the poem G. K. Chesterton wrote about the battle: http://www.bartleby.com/103/91.html
To listen to a chant of the Templars as they march to war: http://www.youtube.com/watch?v=M0d4qM7gCH8