system
Given the following post, respond as if you're commenting on Reddit:
human
[ELI5] Globalisation

What it is, why are some people against it, advantages and disadvantages. Thanks in advance.
gpt
Globalization, broadly speaking, is the movement of the international economy to a freer market, or a market with less trade barriers. 

This has several implications. One of them being it increases the profits of specialization. Specialization is a concept in economy that describes a method of production for an economy, where one concentrates on producing something they excel at (e.g., oil) in return for things they need but can't produce themselves (e.g., weapons, food, consumer products). We all do this to a degree, and specialization is what moved us out of the middle ages into the modern economy. A doctor specializes in the skill of healing, and he trades his skills and services in return for things he otherwise can't produce himself (a house, his car, the milk he drinks). If a doctor had to be self-sufficient, he would also have to own farmland, acquire machinery, gain access to materials, and learn the knowledge required to manipulate them.

However, too much specialization can be bad too. For example, an island nation in the Pacific has a particular soil type that is most excellent in producing coffee. So they start to specialize in the coffee trade. As they discover there is money to be earned in coffee, and as they receive money from the coffee they are selling, this nation decides to expand their coffee industry. Soon, the coffee industry may become so big it accounts for 50% of the nation's GDP (the amount of products they produce). This becomes dangerous, because if a natural disaster occurs, and their coffee crop is wiped out, the entire nation's economy will collapse, and its people can now no longer afford food, nor do they have the means to grow it themselves. 

Of course, countries never fully specialize in their most profitable crop/product because of things such as trade barriers. These can be natural, such as the cost of shipping food across an ocean, or be artificial, such as a government imposing import tariffs (they tax goods coming in from overseas). So, even though U.S. might be able to produce rice at $1/ton, after the costs of transport + tariffs, this cost may now rise to $2/ton. If our imaginary nation can produce rice at $1.5/ton, it's not as efficient as the U.S., but it's still cheaper. Therefore, because of things like trade barriers, nations won't fully specialize. Now, you can see what might happen if these trade barriers are removed. In a real world example, the U.S. signed a treaty with the Mexico that removed trade tariffs. As a result, many Mexican farmers lost their livelihoods because they couldn't produce as cheaply as American agricultural corporations could. To summarize, globalization, or the reduction of trade barriers give incentives for nations to further specialize. This further specialization creates more exposure for the national economy to crisis and mishaps.

This leads into the second major implication. As trade barriers are lowered, the competitiveness of companies overseas are increased. Remember, the rice farmer on our imaginary pacific island nation is 'protected' by the trade barrier. With it, his $1.5/ton rice is competing with $2/ton import rice. Without it, he is competing with $1/ton import rice. Although this means the islander inhabitants get to buy cheaper rice, this also drives out local rice farmers and lead them to rely upon foreign rice suppliers. In the real world, the implications are that mutli-national corporations and conglomerates are given more power and more access in local markets. Due to their vast scale, they are able to outproduce everyone else, and thus do so at a lower price (this is know as the economy of scale). Although the local population are now given access to cheaper products, they loose power and become dependent on a foreign entity. 

There are many other factors at play here, but these are the main ones in very dumbed down terms.

EDIT: grammar and spelling.