During the 20th century, industrialization was progressing all through out the world at a massively fast pace. However, sustainable development as a concept hadn't been born at that time. As such, factories were solely focused on increasing the productivity of man and machines and creating more products. They were least concerned with the fumes that emitted out of the factories or the slews that drained into the rivers. The growing population was attracted to the city industries and therefore flocked to the cities in search of work.

"As such, it was said that problems like population, urbanisation, industrialisation and increased use of science and technology threatened the very survival of mankind."

However this statement is not entirely true in itself. The statement misses one important key, that is industrialisation or urbanisation by itself are not harmful or detrimental to man or the environment. It is man's apathy to the environment and letting it suffer by way of industrialisation, over population and urbanisation that was the issue.

They issue that should have been focused on by the countries which were rapidly urbanising or industrialising was how they could do so, without polluting the environment.

However, the growing degradation of the environment, rising green house gases and polluted rivers and seas, led to developed countries taking a serious note on it and the organization of United Nations Conference on the Human Environment by the United Nations General Assembly, which was held in Stockholm, Sweden in the year 1972. The conference is famously known as the Stockholm Conference and it resulted in the participant countries accepting a declaration consisting of 26 principles, which are known as the Stockholm Declaration.
The principles are:

1. Human rights must be asserted, apartheid and colonialism condemned.
2. Natural resources must be safeguarded.
3. The Earth's capacity to produce renewable resources must be maintained.
4. Wildlife must be safeguarded.
5. Non-renewable resources must be shared and not exhausted.
6. Pollution must not exceed the environment's capacity to clean itself.
7. Damaging oceanic pollution must be prevented.
8. Development is needed to improve the environment.
9. Developing countries therefore need assistance.
10. Developing countries need reasonable prices for exports to carry out environmental management.
11. Environment policy must not hamper development.
12. Developing countries need money to develop environmental safeguards.
13. Integrated development planning is needed.
14. Rational planning should resolve conflicts between environment and development
15. Human settlements must be planned to eliminate environmental problems.
16. Governments should plan their own appropriate population policies.
17. National institutions must plan development of states' natural resources.
18. Science and technology must be used to improve the environment.
19. Environmental education is essential.
20. Environmental research must be promoted, particularly in developing countries.
21. States may exploit their resources as they wish but must not endanger other countries' territories.
22. International law relating to liability of states due to pollution must be furthered.
23. Each nation must establish its own standards.
24. There must be cooperation on international issues.
25. International organizations should assist in the improvement of the environment.
26. Weapons of mass destruction must not be used and be eliminated.

The most landmark feature of this statute was that it entailed heavy obligations on part of the developed nations as they were responsible for centuries of environmental pollution. However due to this provision, several developed countries dropped out. USA never ratified the declaration and Canada backed out of the Declaration in 2012. Still, the declaration sets a great stepping stone in the coming together of the countries of the world to stop environmental pollution.

The next landmark progress that boosted the international momentum with regards to curbing environmental pollution and strengthening international environmental laws was the Rio declaration. The Rio Declaration on Environment and Development, often shortened to Rio Declaration, was a short document produced at the 1992 United Nations "Conference on Environment and Development" (UNCED), informally known as the Earth Summit. The Rio Declaration consisted of 27 principles intended to guide countries in future sustainable development. It was signed by over 175 countries.

Some of the 27 principles are:

• Principle 1 - Human beings are at the centre of concerns for sustainable development. They are entitled to a healthy and productive life in harmony with nature.
• Principle 2 - States have, in accordance with the Charter of the United Nations and the principles of international law, the sovereign right to exploit their own resources pursuant to their own environmental and developmental policies, and the responsibility to ensure that activities within their jurisdiction or control do not cause damage to the environment of other States or of areas beyond the limits of national jurisdiction.
• Principle 3 - The right to development must be fulfilled so as to equitably meet developmental and environmental needs of present and future generations.
• Principle 4 - In order to achieve sustainable development, environmental protection shall constitute an integral part of the development process and cannot be considered in isolation from it.
• Principle 5 - All States and all people shall cooperate in the essential task of eradicating poverty as an indispensable requirement for sustainable development, in order to decrease the disparities in standards of living and better meet the needs of the majority of the people of the world.
• Principle 6 - The special situation and needs of developing countries, particularly the least developed and those most environmentally vulnerable, shall be given special priority. International actions in the field of environment and development should also address the interests and needs of all countries.
• Principle 7 - States shall cooperate in a spirit of global partnership to conserve, protect and restore the health and integrity of the Earth's ecosystem. In view of the different contributions to global environmental degradation, States have common but differentiated responsibilities. The developed countries acknowledge the responsibility that they bear in the international pursuit to sustainable development in view of the pressures their societies place on the global environment and of the technologies and financial resources they command.
• Principle 8 - To achieve sustainable development and a higher quality of life for all people, States should reduce and eliminate unsustainable patterns of production and consumption and promote appropriate demographic policies.
• Principle 9 - States should cooperate to strengthen endogenous capacity-building for sustainable development by improving scientific understanding through exchanges of scientific and technological knowledge, and by enhancing the development, adaptation, diffusion and transfer of technologies, including new and innovative technologies.
• Principle 10 � States shall facilitate and encourage public awareness and participation by making information widely available. Effective access to judicial and administrative proceedings, including redress and remedy, shall be provided.

These are just 10 of the 27 principles declared in the Rio declaration.
Subsequent to it was the the Kyoto Protocol which is an international treaty that extended the 1992 United Nations Framework Convention on Climate Change (UNFCCC) focusing on state parties to reduce greenhouse gas emissions. The Kyoto Protocol implemented the objective of the UNFCCC to reduce the onset of global warming by reducing greenhouse gas concentrations in the atmosphere to "a level that would prevent dangerous anthropogenic interference with the climate system" and worked on reducing the levels of gases like Carbon dioxide (CO2), Methane (CH4), Nitrous oxide (N2O), Hydrofluorocarbons (HFCs), Perfluorocarbons (PFCs), and Sulphur hexafluoride (SF6) from the atmosphere.

Then there was the Paris agreement held in 2015. It was an agreement within the United Nations Framework Convention on Climate Change (UNFCCC), dealing with greenhouse-gas-emissions mitigation, adaptation, and finance, signed in 2016.

The Paris Agreement, ensured that each country has to determine, plan, and regularly report on the contribution that it is regularly making so as to mitigate global warming. However in 2020, USA backed out of the agreement.

Needless to say, the agreement was a great step in enhancing the international momentum to making laws in curbing environmental pollution and degradation.