Three main things:

1. First mover advantage - There were others around the same time - Jaiku, Pownce, Plurk, Identi.ca, etc. - but they didn't get critical mass quickly enough.

2. "Disruptive" product - Who knew a new online platform could totally transform the way we communicate and consume content.

3. Open API to encourage ancillary app development. The rush for 3rd-party app integrations created a zeitgeist of innovation (and future acquisitions for the company).

I'd also say that the simplicity and focus on limited features was an advantage. And nimble response to its early adopter usage patterns and requests (ex: integrating "retweets" and hashtags into the product feature set).

(For context, I started an early Internet company in 1995, a social media marketing firm in 2005 before we called it social media and began using Twitter March 2007.)

I wouldn't say they avoided competition. They compete with fb :)

Twitter was able to avoid competition in becoming a dominant company by playing the monopoly card. There are many ways to create a monopoly, and most of them rely on some form of assistance from the government. Perhaps the easiest way to become a monopoly is by the government granting a company exclusive rights to provide goods or services. The British East India Company, to which the British government granted exclusive rights to import goods to Britain from India in 1600, may be one of the best-known monopolies created in this manner. In a similar manner, nationalization is another way to create a monopoly.
Because the government has laws in place to protect intellectual property, the creators of that property are given monopoly power over things like ideas, concepts, designs, storylines, songs or even short melodies. Having access to a scarce resource is another way to create a monopoly. While the government eventually broke up the monopoly, it took several tries and nearly 20 years to do so. While governments usually try to prevent monopolies, in certain situations, they encourage or even create monopolies themselves.
In many cases, government-created monopolies are intended to result in economies of scale that benefit consumers by keeping costs down. Utility companies that provide water, natural gas or electricity are all examples of entities designed to benefit from economies of scale. Imagine, for example, the cost to consumers if 10 competing water companies each had to dig up the local streets to run proprietary water lines to every house in town. Consumers purchasing from a monopoly often find they are paying unjustifiably high prices for inferior-quality goods.
Also, the customer service associated with monopolies is often poor. For example, if the water company in your area provides poor service, it is not like you have the option of using another provider to help you take a shower and wash your dishes. For these reasons, governments often prefer that consumers have a variety of vendors to choose from when practical. However, monopolies can be equally problematic for would-be business owners as well because the inability to compete with a monopoly can make it impossible to start a new business.
Claiming bringing the two largest food distributors in the country together would create an entity so large and powerful it would stifle competition. If one company completely controls a product or service, that company can charge any price it wants. Consumers who will not or cannot pay the price do not get the product. For reasons both good and bad, the desire and conditions that create monopolies will continue to exist. Accordingly, the battle to properly regulate them to give consumers some degree of choice and competing business the ability to function will also be part of the landscape for decades to come.
Besides if you do have any questions give me a call: https://clarity.fm/joy-brotonath