To conquer any person, society, country or people one must first attack/change their mind.  This is the devils first temptation to any one of us - an idea.  Therefore, to conquer the world, satan had to corrupt men's minds and it has been going on ever since the the height of Catholicism, which was, as Dr James Walsh says, the 13th - the greatest of centuries.  For then, man lived with God as his priority and focus and, because his spiritual life was ordered, everything material was ordered, especially his mind and his outlook on life and truth.  Since the 13th century, the Church has declined and error has grown, and today we are seeing the "fruits" of the errors which satan started planting over 500 years ago.  Most of these errors attacked the mind; for a man who cannot think properly, can easily be corrupted and ruled.  

Here's a top 10 list of modern philosophical errors, in somewhat chronological order.  

1.  Protestantism 1517 - sola scriptura, sola fide and the rise of individualistic spirituality and anti-papacy ideals.
2.  Galileo/Copernicus 1600s - beginnings of science challenging religion.  Denial of the Scriptural account of creation and Biblical truth in general.
3.  Rene Decarte 1600s - father or rationalism, which taught that one could reason to all truth.  Father of subjectivism, which doubts spiritual truths.
4.  John Locke 1600s - father of empiricism and liberalism.  All are born equal and all knowledge is from experience.  Denial of soul's powers.
5.  Fɾҽҽmαsσɳɾყ / illuminati 1717 - organized political satanism and start of social corruption on a grand scale.  Advance of Gnosticism.
6.  Immanuel Kant 1700s - philosophical father of realism, which taught that only things which can be sensed are real.  Spiritual things are subjective.
7.  French Revolution 1789 and rise of democratic governments, and anti-monarchical ideals.  First govt based on atheistic humanism.
8.  Evolution 1850s - start of atheism, revival of paganism and the worship of science over religion.  Denial of the soul and God's creation.
9.  Karl Marx/Communism 1917 - atheism and anti-catholicism as actual political movements.  Idea that man is owned by the state, which rules all.  
10.  Vatican 2 - ...You could do 10 points just on V2 alone...  The most far-reaching error (because it corrupts both catholics and non-catholics) is ecuмenism.  The idea that 'all religions are equal' will lead to the coming one-world religion, which will be the atheistic humanism started at the French Revolution and the necessary religious atmosphere needed for the anti-christ.  Ecuмenism is the logical religious conclusion of rationalism and liberalism.

You could easily do a further Top 10 of non-philosophical errors which have corrupted modern man:
1.  Birth Control
2.  State supported Abortion
3.  State supported Divorce
4.  State run public schools
5.  Protestant King James Bible and the challenging of the Church and Scriptural truth by organized error.  Church influence in science is destroyed.
6.  Feminism - Women voting rights and women working outside the home.  Conflict of the sexes; destruction of God-ordained gender roles.
7.  Usury - Along with Calvinism, the rise of 'time is money' thinking and the value of money/capital over labor and effort.  Rise of Central Banks.
8.  Industrialization - beginning of decline of farm life and rise of mega cities.  Splitting of man from his family to work outside the home.
9.  Capitalism - The "other side of the coin" to communism.  Worship of money vs worship of the State.  Both ideals lead away from God and to hell.
10. The Beatles/Gone with the Wind - rise of satanic music, Hollywood propaganda and emotionalism in music, movies, culture and the home.