A rapid population expansion occurred just after the turn of the 20th century, when Sydney became home to one of North America's main steel mills.

A few years into the war (1781) there was a naval engagement between two French ships and a British convoy off Sydney, Nova Scotia, near Spanish River, Cape Breton.

[2] The convoy, which consisted of 18 merchant vessels, including nine colliers and four supply ships, was bound for Spanish River on Cape Breton Island to pick up coal for delivery to Halifax.

[10] The vice regal residence was located to the east of military grounds along DesBarres Street (and since re-developed as a residential area).

The colony was disbanded and merged with neighbouring Nova Scotia as part of the British government's desire to develop the abundant coal fields surrounding Sydney Harbour; the leases being held by the Duke of York.

Once a Royal Canadian Navy base, HMCS Protector, was established to stage supply convoys bound for Europe.

[14] Convoy SC 7 typified the dangers inherent with the Nazi U-boats off the coast of Cape Breton and Newfoundland during the Battle of the Atlantic, when 20 of the 35 merchant cargo vessels were sunk on their journey to England.

Two notable shipping attacks occurred during this battle: the sinking of the train ferry SS Caribou in October 1942 on its way from North Sydney to Port aux Basques, Newfoundland;[15] and the sinking of the Sydney-based HMCS Shawinigan on 24 November 1944 in the Cabot Strait, near Cape North, on Cape Breton Island.

[18] Both the provincial and federal government were involved in negotiating with the steel plant's owners, when Cape Breton's citizens held the largest protest in the city's history on 19 November 1967: "The Parade of Concern.

Smith and federal Health Minister, and Cape Breton MP, Allan J. MacEachen spoke to the crowd and assured them that their respective governments were going to help.

Forced to diversify its economy after the closures of the steel plant and coal industries, Sydney has examined a variety of economic development possibilities including tourism and culture, light manufacturing and information technology.

Cleaning up the former steel plant, and the toxic Sydney Tar Ponds it left behind in Muggah's Creek, were a source of controversy due to its health effects on residents, although it has provided some employment since SYSCO closed.

Sydney experiences a cool summer, and windy, wet and stormy winter, version of a humid continental climate (Köppen Dfb) that is significantly moderated by the community's proximity to the Atlantic Ocean.

Annual temperatures are instead rather similar to areas around the Baltic Sea in north-eastern Europe at much higher latitudes, although Sydney's seasonal lag is stronger.

Although Sydney has some maritime influence, similar latitudes on the other side of the Atlantic have significantly milder climates in all seasons except summer.

Sydney is in the direct path of fall and winter storms (in the U.S., called nor'easters) migrating from the U.S. Northeastern and New England states; these storms can attain tremendous intensity by the time they approach Sydney, with high winds, heavy snow, ice and/or rain events common, primarily from October to February.

Overall, Sydney's climate is moderately cold and strikingly variable, wet, stormy and windy from fall to early spring (October to March), and more stable and drier in summer (June to August).

Sydney suffered an economic decline for several decades in the later part of the 20th century as local coal and steel industries underwent significant changes.

In one part of Whitney Pier, residents of Frederick St. discovered contamination within several homes and in surrounding soil, including a toxic orange substance oozing into local basements.

Testing of the substance lasted over a year and many were outraged by delays, although some residents were subsequently relocated to a safer residential area nearby.

High unemployment and lack of opportunities have resulted in many educated young people leaving the community for jobs in other parts of Canada and the US.

Demographic changes, including an aging population and decrease in the birth rate, have affected the area's economic outlook.

The dredge, which is expected to lead to commercialization of the port, is purported to create hundreds of jobs in the area, and position Sydney as a world-class harbour facility.

Other important investments that have helped position Sydney as an eastern hub of Nova Scotia include the twinning of Highway 125 and the creation of the Centre for Sustainability in the Environment at nearby Cape Breton University, which draws hundreds of international students each year.

However, Sydney has witnessed a revival as a result of significant government investment in cruise ship facilities and a waterfront revitalization plan which has seen a boardwalk and marinas constructed, and the world's largest fiddle.

Sydney's tourism draw is increasingly linked to its cultural asset as being the urban heart of Cape Breton Island.

Its population is a diverse mixture of nationalities which contributes to various Scottish, Acadian, African Canadian and eastern European cultural events being held throughout the year.

The annual Celtic Colours International Festival is held throughout Cape Breton Island in October, with some of the concerts taking place in Sydney.

The Cape Breton and Central Nova Scotia Railway makes Sydney its eastern terminus and provides rail connections to CN in Truro via Port Hawkesbury.

The JA Douglas McCurdy Sydney Airport is located several kilometres outside the former city limits in the neighbouring community of Reserve Mines.