A travel advisory about a country or region is issued by the government of another country to provide its travelling citizens and expatriates with information and advice on situations that may affect their safety and well-being.

If the country you will be visiting becomes subject to a travel advisory, your travel health insurance or your trip cancellation insurance may be affected. You may also wish to consult the advice of governments other than your own, but their advice is designed for their citizens. As one example, American citizens in the Middle East might face different situations from Europeans or Arabs.

Understand
While extensive information on everything from armed conflict to wildfires to natural disasters is available from multiple sources, a widely cited group of travel advisories is published by the diplomatic corps of various nations. These differ in tone from the flood of information delivered by mass media as the twenty-four hour news cycle presents events as nominally-neutral facts (“A seismological expedition rode into Pompeii today to investigate quakes which may signal an imminent volcanic eruption…”) while a travel advisory is a political construct which represents a summary of the situation on the ground, as an opinion and a form of advice (“The Pharoah of Egypt advises all loyal citizens journeying thorugh Imperial Rome to avoid all travel to Pompeii…”).

The respective national diplomatic corps of the principal political and industrial powers usually establish local presence in many far-flung lands, where they dedicate substantial resources to obtaining up-to-date information on the situation on the ground. If a destination’s infrastructure has been completely destroyed by war or disaster, diplomats who serve or work in the stricken areas will be well aware of the local situation.

Nonetheless, there are some caveats when relying on governments as a source of advisories:

Advisories are merely a brief summary of the political situation in one country. The views presented are often cursory, general and oversimplified compared to the more detailed information available elsewhere. They will explain that “Somalia is a war zone” but sometimes will not explain the full context.
Advisories tend to contain generic advice which could apply anywhere (“don’t leave valuables on open display in your unlocked vehicle”) and are prone to pointing out the blindingly obvious. There’s also a tendency to oversimplify. As one example, the distinction between peaceful protest and violent protest is often lost on governments that see any large gathering as a potentially-deadly riot waiting to happen.
Advisories are intended for international travel only. The US State Department won’t warn if an individual Chicago neigbourhood becomes dangerously crime-ridden but will eagerly alert voyagers to a Mexican drug gang running roughshod across Tijuana. That doesn’t mean that some random Nebraskan couldn’t run into serious trouble on the wrong side of an inner city in the US Rust Belt, just that there is no consular assistance for purely-domestic travel.
Governments are political entities. They are often reticent to offend a major trading partner, quick to condemn a political adversary or slow to judge an ally. There are many instances throughout the Cold War era when both Communist-bloc and Western governments were actively propping up overseas dictators themselves. This often meant turning a blind eye; for instance, Roosevelt’s Secretary of State (Sumner Welles) supposedly said “Somoza’s a bastard!” and Roosevelt replied “Yes, but he’s our bastard.”
Advisories focus unduly on issues relating to government and diplomacy, such as the inability of Western voyagers to Crimea to obtain consular assistance (Western governments are obliged de jure to respect the territorial integrity of Ukraine, while de facto Crimea has been occupied by Russia since 2014).
Conversely, natural hazards (such as attacks by dangerous animals) may receive less attention than political issues (like riots or terrorism).
Advisories tend to broadly cover entire countries or large regions. It is often unclear what impact a purely-local issue (like Hong Kong’s warning “On 1 October 2017, attacks occurred in the city of Edmonton, Alberta. A police officer was stabbed and a few pedestrians were hit by a car…”) will have on voyagers bound for some other region of the country.
Travel advisories are often more alarmist than other sources. (Many pages on the US State Department’s travel advisory site advise prospective travelers to high-risk nations to “Draft a will and designate appropriate insurance beneficiaries and/or power of attorney.”) They want to reduce the risk of citizens coming to harm, because it could cost money, time and effort for an embassy to attempt to get their citizens relocated/rescued/bailed out or the diplomatic incidents wayward voyagers not knowing how to behave might cause.

Still, erring on the side of caution can never do harm and there is often a lot of valuable advice that is usually fairly up to date in major travel advisories.

It’s useful to see what individual governments are saying about a destination, but don’t use this as a substitute for doing your own research to see what news reports, online reviews or other sources – including the opinions of other voyagers – are saying about a place which you are considering for travel.

Government travel advisories
Various governments have placed their advisories on-line, freely available to all. The sites vary in quality; some are merely a collection of press releases, while others have one dedicated page for each destination country – typically ranking each on a scale ranging from “exercise normal precautions” to “avoid non-essential travel” or “avoid all travel”.