Planning to RSP into US based ETFs over a long term horizon, should i wait till the US market crashes further?

It is definitely difficult to tell when the bottom is and if the market will crash even further, hence many will advocate adopting a DCA approach - if it goes higher you wouldn't feel like you missed the lower boat, if it goes lower you can continue to average down your entry price.

As for the US market, it should still continue to be the dominant market after this epidemic (for which no one knows will happen for how long). At present, US markets accounted for 54% of world stocks - this figure varies across sources but I found this via Statista as of Jan 2020. Miles ahead of other countries in single digit %, it could take decades for another power to dethrone US. Some say 2050, but let's see.

When you mentioned investing over "long-term horizon", does that horizon include e present?

The FEDs seem determined to prop up the stock market as much as it can.

a drastic drop a few weeks ago, and the stock market has recovered so much strongly now...... perhaps its time to enter soon

Nobody really can predict anything. just invest regularly independent of perceived crisis or anything. what not to do, You can read here:

https://seedly.sg/questions/what-is-your-genera...