Historically the 3 major threats to liberty have been: (1) monarchy, (2) socialism (or communism), and (3) Islam.
Monarchy was the original threat to liberty. "Monarchy" is considered to be any society which is lead by an individual or a small group of individuals, usually the monarch and his family and closest aids. This may be the chief of just a small tribe, the king of an independent nation, the ruler of a nation that is part of an empire, or an emporer himself that rules over a collecion of nations. The position of monarch is most commonly passed down from father to oldest son upon the death or severe disability of the father. In more rare circumstance, the role of monarch is passed to a son other than the oldest, or to a wife, daughter, or other relative when there are no sons able to serve. However, quite often in history the rold of monarch has been usurped by a relative not in the line of succession, or by another relative, or another powerful individual, or even by an invading nation.
The monarchy is comprised of the one ruling individual or group of individuals that makes and enforces the laws of their nation with little or no consent by those over who they rule. Often, all land and other goods of the state are considered to be the personal property of the monarch(s) to be used as he or she sees fit. Those who live under the monarchs rule are considered to be the "subjects" of the monarch. The power of a monarch is not necessarily absolute. A monarch will often have to deal with other powerful sectors within his own nation including religious institutions, respected military leaders with their own troops, plus other wealthy indivuals who the monarch may need to rely on for sources of funding, troops for battle, and even cooperation to keep from being overthrown.
Starting with the American Revolution of 1776, monarchy entered a period of rapid decline with most major nations around the world discarding this form of government. There are few governments in the world today that retain monarchy as their form of rule. A few nations that have still retained some form of monarchy have change their monarch to be more of a role of public relations with little or no power over actual governance. monarchy, the form of government that was once the most power obstacle to liberty, is little threat to liberty anywhere in the world anymore.
After the Amerian Revolution in 1776 and over the next century or so, peoples across much of the globe started throwing off their monarchy forms of government, often in violent revolutions. The concept that citizens have the right to govern themselves became the norm. But, the form such a government should take where people govern themselves became hotly debated, and a debate that was to lead to much bloodshed for more than two centuries and still continues today.
Starting in the year 1215 with the Magna Carta, British citizens had already started enjoying a greater degree of liberty with restrictions being placed on the monarchy. But in the British colonies in American which first started being established in the early 1600's, colonists were enjoying an even greater amount of liberty. With a distance of over 3,000 miles from Britain to America, colonists had to be able to be self-reliant and independent just to be able to survive.
Thus, at the time of the American Revolution in 1776, the colonists already had been enjoying a great deal of liberty and self-governance for almost two centuries. The government that was formed after the revolution pretty much codified the way people had already been living. It allowed people to continue to manange their own lives with little government interference. The role of the government was pretty much kept to just keeping the peace and protecting its citizens from invasion.
Over the next century, many governments that abandoned monarchy followed the American example of limiting the role of government and allowing its citizens the liberty to manage their lives as they wished.
But not evolutions away from monarchy took this path. Many nations instead took the path of replacing the monarchy with "citizens committees" who retained most of the power of the monarchy they replaced, but who were charged with executing these powers for the benefit of the citizens of the nation.
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Probably all religions were once a major obstacle to liberty, both in theocratic states and in states where religion had a major influence in governance. This was certainly true during the reign of the Holy Roman Empire when the Pope would crown the kings of every Christian nation. It was also certainly true during both the Spanish Inquisition and the Spanish conquest and colonization of the Americas. And it was most certainly true during the Christian Crusades.
With the dissolution of the Holy Roman Empire and the overthrow of monarchies, Christianity lost almost all of its political power and influence in governance. The Jewish Kingdoms had already ended a thousand years early after being conquered by the Greeks and the Jewish diaspora. So already before even the start of the nineteenth century, Christianity and Judaism had ceased to be any sort of major obstacle to liberty.
Islam, however, is a different story. Islam continues to play a very significant role in many governments including some that are actual theocracies. There may even be more Muslims now than ever trying to create a new Islamic State. ISIS / ISIL, or the "Islamic State", as they prefer to call themselves, believe they have already created or restored the Islamic State, at least in part.
The tenants of some versions of Sharia Law are definitely opposite of the principles of liberty. The Arabic term "Islam" itself is usually translated as "submission"; submission of desires to the will of God. This itself can be viewed as against the principles of liberty depending on what one thinks the "will of God" wants them to do.
Some versions of Sharia Law condem homosexuals, subjugate women and believe that those who are not Muslim must either convert or pay tribute to Islam. If that is the version of Sharia Law that one follows, then that manner of practicing Islam is certainly a threat to liberty.