Queens experienced tremendous growth leading up to the 20th Century, as factories were built along the East River and Newton Creek. William Steinway opened up his piano factory in 1870, including several docks, sawmills, a foundry and housing for his workers that came to be called Steinway Village (the Steinway mansion still stands today and is on the market for a cool $1.9 million). Steinway even built an amusement park called North Beach, a resort that included an ill-fated beer hall that couldn't survive Prohibition; the land was turned into the North Beach Airport, later expanded and renamed LaGuardia Airport. In 1879, the Long Island Terra Cotta Company was established in Ravenswood, which quickly became a heavily industrialized area (the company's headquarters, built in 1892, still sits in the shadow of the Queensboro Bridge).

The residential population grew tremendously as Queens was connected to Manhattan; the Queensboro Bridge opened in 1909 (with a connection to the Second Avenue El, plus a trolley to Roosevelt Island), the Long Island Railroad's electrified tunnels to Penn Station opened in 1910, the Hell Gate Bridge began carrying freight rail in 1916, and in 1917 the Flushing and Astoria lines began joint operation. Real estate developers brought up large tracts of land near the new lines, building apartment buildings and row houses and apartments in anticipation of a surge in population (Sunnyside Gardens, opened in 1924, is an excellent example of one of those residential developments). As soon as a few rapid transit lines extended into Queens, residents began clamoring for more connections, which were provided for as part of the new Independent Subway; the first stations of the IND Queens Boulevard and Crosstown lines opened in 1933. Neighborhoods grew quickly, and in many cases became strong ethnic enclaves (e.g. Germans in Astoria, Irish in Woodside, and later Indians in Jackson Heights and Chinese in Flushing).

This period was also the heyday of parkway and expressway building, under the auspices of Robert Moses, head of the Bridge and Tunnel Authority. The Triborough Bridge was opened in 1936, and the Whitestone Bridge in 1939 (the Throggs Neck was opened in 1961), connecting Queens to the Bronx and bringing more people into the borough (as well as to the suburbs beyond). There were many existing factories along the Newton Creek, and with the advent of trucking more sprung up, particularly in Long Island City, Ravenswood and Astoria. According to one source, out of 1,700 factories and warehouses in Queens, over 1,400 of them were in the Long Island City area alone!

Leading up to the World's Fair of 1939 in Flushing Meadows Park, developers built buildings at an incredible pace; during the latter half of the 1930s, more than 70% of new construction was in Queens. Interestingly, however, after this period, several new subway lines were planned but never constructed, including a permanent connection from the Queens Boulevard Line to the World's Fair (after the fair the connection was dismantled, although part of the right-of-way is still there) and an extension of the Flushing line to Great Neck. The population of the borough grew by nearly 500,000 people from 1930 to 1950 (1,079,129 in 1930 to 1,550,849 in 1950), the highest rate of growth in the city.

I recently wrote an essay on the Rockaways for a class I took. Ill post some of it here.

Rockaway beach was founded by Michael Holland and Louis Hammel around eighteen seventy eight. Hammel gave some of his land to the raildroad company in order to bring people to his neighborhood. In eighteen ninety-eight Rockaway Beach joined New York City as a part of Queens. Before the railroad opened up the Rockaways were an exclusive place for the wealthy. After it opened up it became known as “New York’s Playground” due to the amusement park Rockaways’ Playland. The amusement park combined with the beach, trains, and ferries made the area very profitable and a major job producer. The amusement park even had a copy of the famous Coney Island Cyclone called the Atom Smasher. The community’s accessibility without the need of a car was a large part of its success, but also led to its downfall.

Robert Moses, arguably New York City’s most known Parks Commissioner, wanted to construct highways and roads all over the city. Under him the Marine Parkway Bridge and the Cross Bay Veterans Memorial Bridge were constructed in order to connect the peninsula to Brooklyn and allow people to come and go easily by car. Moses also wanted to build a highway through the peninsula and directly hurt the community. Houses were literally cut in half in order to build the highway. It was started, but never finished. His other projects hurt the community by taking away people from the beach and park there. The new roads and the fact more people had cars allowed people to travel to Jones Beach in Long Island and the New York Aquarium. This marked the decline of the Rockaway Beach Community.

In order to make Rockaway more appealing and new the City of New York’s Housing Authority built the Hammel Houses, named after the areas founder. These houses brought the value of the area down due to poorer people moving into them. So much public housing was constructed in the Rockaways that by nineteen seventy-five, fifty-seven percent of public housing in Queens was there. The bungalow owners who would usually rent out to summer vacationers did not want to renovate and rent to them. Instead, they rented to very poor families. The combination of public housing and lack of private investors led to a decrease in the desirability of the area.

The rest of it was about more recent times and not really relevant to your question. Hope this helped.