During the centuries of the crusades, all sorts of slanders were invented against Prophet Muhammad (pbuh). But with the birth of the modern age, marked with religious tolerance and freedom of thought, there has been a great change in the approach of Western authors in their delineation of his life and character. The views of some non-Muslim scholars regarding Prophet Muhammad, given at the end, justify this opinion.
But the West has still to go a step forward to discover the greatest reality about Muhammad 
and that is his being the true and the last Prophet of God for the whole humanity. In spite of all its objectivity and enlightenment there has been no sincere and objective attempt by the West to understand the Prophethood of Muhammad (pbuh). It is so strange that very glowing tributes are paid to him for his integrity and achievement but his claim of being the Prophet of God has been rejected explicitly or implicitly. It is here that a searching of the heart is required, and a review of the so-called objectivity is needed. The following glaring facts from the life of Muhammad (pbuh) have been furnished to facilitate an unbiased, logical and objective decision regarding his Prophethood.
Up to the age of forty, Muhammad was not known as a statesman, a preacher or an orator. He was never seen discussing the principles of metaphysics, ethics, law, politics, economics or sociology. No doubt he possessed an excellent character, charming manners and was highly cultured. Yet there was nothing so deeply striking and so radically extraordinary in him that would make men expect something great and revolutionary from him in the future. But when he came out of the Cave (HIRA) with a new message, he was completely transformed. Is it possible for such a person of the above qualities to turn all of a sudden into 'an impostor' and claim to be the Prophet of Allah and invite all the rage of his people? One might ask: for what reason did he suffer all those hardships? His people offered to accept him as their King and he would leave the preaching of his religion. But he chose to refuse their tempting offers and go on preaching his religion single-handedly in face of all kinds of insults, social boycott and even physical assault by his own people. Was it not only God's support and his firm will to disseminate the message of Allah and his deep-rooted belief that ultimately Islam would emerge as the only way of life for humanity, that he stood like a mountain in the face of all opposition and conspiracies to eliminate him? Furthermore, had he come with a design of rivalry with the Christians and the Jews, why should he have made belief in Jesus Christ and Moses and other Prophets of God (peace be upon them), a basic requirement of faith without which no one could be a Muslim?
Is it not an incontrovertible proof of his Prophethood that in spite of being unlettered and having led a very normal and quiet life for forty years, when he began preaching his message, all of Arabia stood in awe and wonder and was bewitched by his wonderful eloquence and oratory? It was so matchless that the whole legion of Arab poets, preachers and orators of the highest calibre failed to bring forth its equivalent. And above all, how could he then pronounce truths of a scientific nature contained in the Qur'an that no other human being could possible have developed at that time?
Last but not least, why did he lead a hard life even after gaining power and authority? Just ponder over the words he uttered while dying: "We the community of the Prophets are not inherited. Whatever we leave is for charity."
As a matter of fact, Muhammad (pbuh) is the last link of the chain of Prophets sent in different lands and times since the very beginning of the human life on this planet. Read the following writings of the Western authors:
"If greatness of purpose, smallness of means, and astounding results are the three criteria of human genius, who could dare to compare any great man in modern history with Muhammad? The most famous men created arms, laws and empires only. They founded, if anything at all, no more than material powers which often crumbled away before their eyes. This man moved not only armies, legislations, empires, peoples and dynasties, but millions of men in one-third of the then inhabited world; and more than that, he moved the altars, the gods, the religions, the ideas, the beliefs and souls. . . his forbearance in victory, his ambition, which was entirely devoted to one idea and in no manner striving for an empire; his endless prayers, his mystic conversations with God, his death and his triumph after death; all these attest not to an imposture but to a firm conviction which gave him the power to restore a dogma. This dogma was twofold, the unity of God and the immateriality of God; the former telling what God is, the latter telling what God is not; the one overthrowing false gods with the sword, the other starting an idea with words."
"Philosopher, orator, apostle, legislator, warrior, conqueror of ideas, restorer of rational dogmas, of a cult without images; the founder of twenty terrestrial empires and of one spiritual empire, that is Muhammad. As regards all standards by which human greatness may be measured, we may well ask, is there any man greater than he?"
Lamartine, HISTOIRE DE LA TURQUIE, Paris, 1854, Vol. II, pp. 276-277.
"It is not the propagation but the permanency of his religion that deserves our wonder, the same pure and perfect impression which he engraved at Mecca and Medina is preserved, after the revolutions of twelve centuries by the Indian, the African and the Turkish proselytes of the Koran. . . The Mahometans have uniformly withstood the temptation of reducing the object of their faith an devotion to a level with the senses and imagination of man. 'I believe in One God and Mahomet the Apostle of God' is the simple and invariable profession of Islam. The intellectual image of the Deity has never been degraded by any visible idol; the honours of the prophet have never transgressed the measure of human virtue, and his living precepts have restrained the gratitude of his disciples within the bounds of reason and religion."
Edward Gibbon and Simon Ocklay, HISTORY OF THE SARACEN EMPIRE, London, 1870, p. 54.
"He was Caesar and Pope in one; but he was Pope without Pope's pretensions, Caesar without the legions of Caesar: without a standing army, without a bodyguard, without a palace, without a fixed revenue; if ever any man had the right to say that he ruled by the right divine, it was Mohammed, for he had all the power without its instruments and without its supports."
Bosworth Smith, MOHAMMAD AND MOHAMMADANISM, London, 1874, p. 92.
"It is impossible for anyone who studies the life and character of the great Prophet of Arabia, who knows how he taught and how he lived, to feel anything but reverence for that mighty Prophet, one of the great messengers of the Supreme. And although in what I put to you I shall say many things which may be familiar to many, yet I myself feel whenever I re-read them, a new way of admiration, a new sense of reverence for that mighty Arabian teacher."
Annie Besant, THE LIFE AND TEACHINGS OF MUHAMMAD, Madras,1932, p. 4.
"His readiness to undergo persecutions for his beliefs, the high moral character of the men who believed in him and looked up to him as leader, and the greatness of his ultimate achievement - all argue his fundamental integrity. To suppose Muhammad an impostor raises more problems than it solves. Moreover, none of the great figures of history is so poorly appreciated in the West as Muhammad."
W. Montgomery Watt, MOHAMMAD AT MECCA, Oxford, 1953, p. 52.
"Muhammad, the inspired man who founded Islam, was born about A.D. 570 into an Arabian tribe that worshipped idols. Orphaned at birth, he was always particularly solicitous of the poor and needy, the widow and the orphan, the slave and the downtrodden. At twenty, he was already a successful businessman, and soon became director of camel caravans for a wealthy widow. When he reached twenty-five, his employer, recognizing his merit, proposed marriage. Even though she was fifteen years older, he married her, and as long as she lived, remained a devoted husband.
"Like almost every major prophet before him, Muhammad fought shy of serving as the transmitter of God's word, sensing his own inadequacy. But the angel commanded "Read." So far as we know, Muhammad was unable to read or write, but he began to dictate those inspired words which would soon revolutionize a large segment of the earth: "There is one God."
"In all things Muhammad was profoundly practical. When his beloved son Ibrahim died, an eclipse occurred, and rumours of God's personal condolence quickly arose. Whereupon Muhammad is said to have announced, "An eclipse is a phenomenon of nature. It is foolish to attribute such things to the death or birth of a human being." "At Muhammad's own death an attempt was made to deify him, but the man who was to become his administrative successor killed the hysteria with one of the noblest speeches in religious history: "If there are any among you who worshipped Muhammad, he is dead. But if it is God you worshipped, He lives forever."
James A. Michener, "ISLAM: THE MISUNDERSTOOD RELIGION," in READER'S DIGEST (American edition), May 1955, pp. 68-70.
"My choice of Muhammad to lead the list of the world's most influential persons may surprise some readers and may be questioned by others, but he was the only man in history who was supremely successful on both the religious and secular level."
Michael H. Hart, THE 100: A RANKING OF THE MOST INFLUENTIAL PERSONS IN HISTORY, New York: Hart Publishing Company, Inc., 1978, p. 33.