In affiliate marketing, countries are grouped into tiers based on their development and wealth. These tiers help affiliates know where to focus their efforts. 

Here's a simple breakdown:

• Tier 1 Countries: Developed nations with widespread use of credit cards and frequent online purchases. These markets are very competitive and have higher traffic costs.
• Tier 2 Countries: Developing or emerging markets. These countries are less competitive but still hold significant potential.
• Tier 3 Countries: Undeveloped nations with lower competition and traffic costs.

Different networks might classify countries differently, but here's a general list:

Tier 1 Countries
- Austria, Australia, Belgium, Canada, Switzerland, Germany, Denmark, Finland, France, United Kingdom, Italy, Luxembourg, Netherlands, Norway, New Zealand, Sweden, United States.

Tier 2 Countries
- United Arab Emirates, Argentina, Bangladesh, Bahrain, Brazil, Chile, China, Costa Rica, Cyprus, Czech Republic, Algeria, Estonia, Egypt, Spain, Greece, Hong Kong, Hungary, Indonesia, Ireland, Israel, Iran, Iceland, Japan, Kenya, Kyrgyzstan, South Korea, Kuwait, Kazakhstan, Lithuania, Latvia, Mexico, Malaysia, Peru, Poland, Puerto Rico, Portugal, Qatar, Romania, Serbia, Russia, Saudi Arabia, Singapore, Slovenia, Slovakia, Thailand, Turkey, Taiwan, Ukraine, South Africa.

Tier 3 Countries
- Andorra, Afghanistan, Antigua and Barbuda, Anguilla, Albania, Armenia, Angola, Antarctica, American Samoa, Aruba, Åland Islands, Azerbaijan, Bosnia and Herzegovina, Barbados, Burkina Faso, Bulgaria, Burundi, Benin, Saint Barthélemy, Bermuda, Brunei, Bolivia, Bonaire, Bahamas, Bhutan, Botswana, Belarus, Belize, Cocos Islands, Democratic Republic of the Congo, Central African Republic, Congo, Côte d’Ivoire, Cook Islands, Cameroon, Colombia, Cuba, Cape Verde, Curaçao, Christmas Island, Djibouti, Dominica, Dominican Republic, Ecuador, Eritrea, Ethiopia, Fiji, Falkland Islands, Micronesia, Faroe Islands, Gabon, Grenada, Georgia, French Guiana, Guernsey, Ghana, Gibraltar, Greenland, Gambia, Guinea, Guadeloupe, Equatorial Guinea, Guatemala, Guam, Guinea-Bissau, Guyana, Honduras, Croatia, Haiti, Isle of Man, India, British Indian Ocean Territory, Iraq, Jersey, Jamaica, Jordan, Cambodia, Kiribati, Comoros, Saint Kitts and Nevis, North Korea, Cayman Islands, Laos, Lebanon, Saint Lucia, Liechtenstein, Sri Lanka, Liberia, Lesotho, Libya, Morocco, Monaco, Moldova, Montenegro, Saint Martin, Madagascar, Marshall Islands, North Macedonia, Mali, Myanmar, Mongolia, Macao, Northern Mariana Islands, Martinique, Mauritania, Montserrat, Malta, Mauritius, Maldives, Malawi, Mozambique, Namibia, New Caledonia, Niger, Norfolk Island, Nigeria, Nicaragua, Nepal, Nauru, Niue, Oman, Panama, French Polynesia, Papua New Guinea, Philippines, Pakistan, Saint Pierre and Miquelon, Pitcairn, Palestinian Territory, Palau, Paraguay, Réunion, Rwanda, Solomon Islands, Seychelles, Sudan, Saint Helena, Ascension and Tristan da Cunha, Sierra Leone, San Marino, Senegal, Somalia, Suriname, South Sudan, Sao Tome and Principe, El Salvador, Sint Maarten, Syria, Swaziland, Turks and Caicos Islands, Chad, Togo, Tajikistan, Tokelau, Timor-Leste, Turkmenistan, Tunisia, Tonga, Trinidad and Tobago, Tuvalu, Tanzania, Uganda, Uruguay, Uzbekistan, Vatican City, Saint Vincent and the Grenadines, Venezuela, British Virgin Islands, US Virgin Islands, Vietnam, Vanuatu, Wallis and Futuna, Samoa, Yemen, Mayotte, Zambia, Zimbabwe.

As an affiliate, this classification helps you target your campaigns effectively based on each country's competitiveness and potential returns.