The death rate, also known as mortality rate, is the measure of the number of deaths in a particular population during a particular period of time. Typically, it is calculated as the number of deaths per one thousand people per year. Countries with high mortality rates and relatively low fertility rates and birth rates face the risk of population decline. Death rates vary significantly between countries, and as a rule, developed countries, have a lower death rate than do developing countries, whose health care networks and facilities are less robust. In fact, many of the least developed countries may struggle to provide basic human needs such as potable water, adequate food, and sanitation, which increases the risk of disease and other health complications.

Proper diet and exercise, clean water, and quality health care are the factors that have the greatest impact on mortality rates. Diet and exercise are particularly important: According to the Global Health Data Exchange, cardiovascular disease—which is typically caused by obesity stemming from unhealthy eating habits—was the leading cause of death worldwide from 1990-2019. Diabetes, which is also diet-related, ranked 9th. While it would be reasonable to suspect that developed countries would also be the most obese countries and countries with the highest diabetes rates due to the abundance of processed and "junk" food, they actually tend to also be among the healthiest countries in the world thanks to their more advanced health care systems. That said, even the most modernized health care system has its limits. As such, cancer remains the second-leading cause of death in the world, especially in countries with high rates of smoking and/or alcoholism.

Mortality rates can also see temporary spikes due to less predictable causes of death. Particularly in countries at war or undergoing some other form of civil unrest, gun deaths can boost mortality rates. So can outbreaks of disease. For example, the COVID-19 pandemic is expected to create a significant spike in 2020-21 mortality data.

Bulgaria has the highest mortality rate in the world at 15.4 deaths per 1,000 people. According to the World Health Organization, the causes of death in Bulgaria are similar to those in other European countries, including non-communicable diseases (diseases of the circulatory, digestive, or respiratory systems) and cancers. Bulgaria is currently experiencing a population decline, starting at about 9 million in 2000 and is expected to fall to between 2.8 million and 5 million.

Ukraine has the second-highest mortality rate of 15.2 deaths per 1,000 people. Ukraine is considered to be in a demographic crisis because of its high mortality rate and low birth rate. Overall, Ukraine's health care system is poorly financed, and the country has very low vaccination rates and high rates of diseases and disorders that could be better managed with increased funding. One factor contributing to the mortality rate is the high death rate of working-age males from preventable causes such as alcohol poisoning and smoking. Additionally, Ukraine has one of the fastest-growing HIV/AIDS epidemics globally and suffered one of the worst measles epidemics in the world in 2019.

Latvia's mortality rate is 14.6 per 1,000 people. Latvia also has an underfunded health care system. Although life expectancy has significantly improved in Latvia, the country still lags behind the rest of the European Union, driven by greater exposure to risk factors among men, people with low education, and people with low income. Those with low education levels in Latvia have a life expectancy that is ten years lower than those with high education. Some common risk factors among Latvians are smoking, binge drinking, and obesity.

With a mortality rate of 14.3 deaths per 1,000 people, Lesotho has the world's fourth-highest mortality rate. According to the CDC, the life expectancy at birth in Lesotho is 56 years for females and 52 years for males. The infant mortality rate is 59 per 1,000 live births. The leading causes of death are HIV/AIDS, tuberculosis, stroke, lower respiratory infections, and ischemic heart disease.

Lithuania's death rate is 13.737 deaths per 1,000. The World Health Organization reports that ischemic heart diseases and stroke are the two leading causes of death in Lithuania, with mortality rates four and two times above the average rates in the European Union respectively. Due to high smoking rates, lung cancer is now the third leading cause of death in Lithuania. Lithuania also has the lowest life expectancy in the EU of 74.8 years.

Serbia's death rate is 13.2 per 1,000, the sixth-highest in the world. According to a study, Serbia's mortality rate was lowest in the 1960s, where it was between 8 and 9 deaths per 1,000. During the beginning 21st century, the rate was much higher, reaching 14 deaths per 1,000 at its highest. Demographically, Serbia is one of the oldest nations in Europe, and its aging population has a large role in its death rate. Additionally, chronic non-communicable diseases and cardiovascular disease are the two leading causes of death. Serbia is also among the world's ten countries with the highest smoking rate.

Croatia's mortality rate is 13.1 deaths per 1,000 people. The leading causes of death in Croatia are ischemic heart disease, stroke, Alzheimer's, and lung cancer. About 25% of Croatian citizens smoke tobacco every day, higher than the EU average. Additionally, obesity rates are rising, especially in children, where the rate has grown more than 50% since 2001. While life expectancy has improved since 2000, rising from 74.6 to 78.3, it is still three years below the EU average.

Romania's death rate is the eighth-highest in the world at 13.0 deaths per 1,000. The leading causes of death in Romania are cardiovascular disease, malignant tumors, digestive diseases, accidents, injuries and poisonings, and respiratory diseases. Additionally, the infant mortality rate in Romania is the highest in the EU at about 8 per 1,000. This is often attributed to a shortage of doctors. About 43,000 doctors have left Romania since 2007 to look for opportunities elsewhere.

Georgia has a mortality rate of 12.8 deaths per 1,000. According to the World Health Organization, the leading causes of death are the same in most European nations: cancer, circulatory, respiratory, and digestive diseases, and injuries and poisoning. The premature mortality rate (for individuals under 65) has increased since 2000, with diseases of the circulatory system and cancers cited as the leading causes of death. Several risk factors for non-communicable diseases are common among the Georgian people, including smoking tobacco, alcohol use, and overweight/obesity. The highest risk factors associated with disease in Georgia are dietary risks, high blood pressure, high body mass index, and tobacco use.

Russia finishes the ten countries with the highest death rates with a death rate of 12.7 per 1,000. More than half of the deaths in Russia are caused by cardiovascular disease. The second-most-common cause of death is cancer, followed by suicide, road accidents, homicide, and alcohol poisoning. Alcohol abuse is a significant problem in Russia, especially for men. The life expectancy is 66.4 years for men and 77.2 years for women.

Countries with low mortality rates have more advanced and accessible health care, better-informed citizens, healthier nutritional options, and higher living standards overall. Qatar has the lowest mortality rate in the world at 1.2 deaths per 1,000 people. This low mortality rate can be attributed to Qatar's improved health care system, renowned for its technologically advanced facilities and ability to deliver some of the world's best patient care.