Healthcover insurance has been taken over by a larger international insurance group. Can you tell me what is a business takeover and why would a business be taken over?

A business takeover can be "hostile" or "negotiated".

A business can be up for sale, and another company can buy its assets, (accounts, operations, debt, etc), or, if publicly traded, it can be part of a purchase it didn't want, or "hostile" takeover.

The number of shares in a company someone or some group own determines their voting power. If an outside company can collect enough voting power through outright purchase of shares in the open market and creating shareholder voter blocks from within the corporation, then it is possible for the outside company to force a sale and purchase.

In summary, a business is taken over for a number of reasons, it means that another company now owns all of the assets of the company and all the employees now work for the new company. Unfortunately, often when companies merge, there tends to be a reduction in workforce as positions become "redundant", and cost savings can be made by creating "efficiency" within the new organization.

It is common for companies to buy out or take over others,
The company I am working for, buys out and takes over several companies a year.

Large investment groups buy out other corporations to improve investments and make profits