I wanted an expansion of $(1+x)^n$ and refered Wikipedia but I don't understand why there is a condition of $|x|<1$.
In general, for the series, the condition is not required am I right or am I missing something subtle?
For the ordinary Binomial Theorem, where $n$ is a non-negative integer, there is no $|x|\lt 1$ restriction. In the generalization of the ordinary Binomial Theorem to situations where $n$ is not necessarily a non-negative integer, you get an infinite series that only converges if $|x|\lt 1$.