What was a proposed alternative to Segwit?
Increasing the block size.
What did Segwit solve more than just the scaling issue?
The first intention was to fix a bug in the bitcoin code which we call ‘transaction malleability’. This helped to change small details that modified the transaction ID but not the content. It removes the signature information and stores it outside the base transaction block.
Without the signature info, there is less weight in transactions so it can more fit in a block. In other words, Segwit did not increase the block size but it enabled a greater number of transactions within the 1 MB blocks.
How is Segwit and the Lightning network connected?
Segwit supports the development of second layer protocols like lightning network. The malleability fix made any feature that relied on unconfirmed transactions less risky and easier to design.
Are people, wallets and other services forced to use Segwit?
No, It was a soft fork so they still could use the older version.